The WWI Air War over the Sea

When in August, 1918, I found on visiting France a complete chain of Naval Aviation Stations engaged in a systematic patrol of the waters of that “neck of the bottle” through which our troops and supplies had to pass, I had but to examine the weekly charts of German submarine operations to realize how much our aviators were doing to make these waters safe.

—Franklin D. Roosevelt, Flying Officers of the United States Navy 1917–1919

The protection given to convoys by the presence of accompanying aeroplanes is considerable and though attacks have actually been carried out when D.H.6 aeroplanes have been present, there is no doubt but that the enemy’s submarines have been seriously hampered in their operations by the constant fear of being attacked or sighted by aircraft. In this connection it is of interest to note that the day of greatest losses was one on which aircraft were unable to operate.

—P. R. C. Groves for Director, Air Division, Employment of Aeroplanes for Anti-Submarine Work on North East Coast

Although airmen’s attempts to liaise with the infantry during the war did not always achieve spectacular results, cooperative efforts between aviators and sailors proved far more impressive. At the outset of the war the British Royal Navy implemented a North Sea blockade to prevent merchant ships from reaching their destinations and keep the German surface fleet bottled up in port. The military and geopolitical effects of the blockade, though slow to show themselves, eventually proved effective, slowly bleeding Germany of resources, sapping the morale of the German people, and giving the United States a financial stake in Allied success. More narrowly, the blockade set the tone for the war at sea and for the next four years German naval activity in the Atlantic, the North Sea, the English Channel, and the air war over these waters centered on efforts to either break the blockade or, failing that, to inflict similar damage on the Allies.

Naval aviation differed significantly from its land-based counterpart in the way it interacted with the non-flying forces it supported. Military aviators regularly separated their reconnaissance missions from offensive operations, observing or photographing enemy activities that bombers or the artillery dealt with at a later time. Naval flyers similarly reported their sightings to nearby cooperating surface vessels, but the fleeting nature of floating targets frequently forced naval aviators to attack the targets they spotted immediately.

An American, Eugene Ely, demonstrated what the future held for naval aviation when he successfully flew an airplane off the deck of USS Birmingham in November 1910 and then two months later landed one on the deck of the Pennsylvania.3 The British created an Air Department within the Admiralty and began their own experiments in cooperation between aircraft and naval vessels in 1912, still more than two years before the beginning of the war.4 The duties naval aviators anticipated performing included scouting for the fleet using aircraft carried aboard ships, patrol work along the British coastline, and cooperative missions flown alongside defending flotillas and submarines. In January 1912, Lt. H. A. Williamson, a British submarine officer with an airplane pilot’s license, first proposed using aircraft to patrol against submarines. He hypothesized that, even if unable to attack, the aircraft’s presence would force a targeted submarine to stay completely submerged, thereby reducing its threat. Williamson noted the French were also experimenting with this idea. Later developments would prove Williamson’s predictions correct. Within six months early results of the British tests convinced the Royal Navy’s Submarine Committee that aircraft showed “promise of providing a valuable anti-submarine weapon.” On September 11, 1912, Capt. Murray Sueter, director of the British Royal Navy’s Air Department, submitted an aircraft development proposal to the Board of Admiralty in which he listed potential duties that included “assisting destroyers to detect and destroy submarines.” Sueter’s plan encompassed suggestions for a network of coastal air stations at various locations around the British coast, including Calshot, Dundee, Eastchurch, Felixstowe, Fort Grange, the Isle of Grain, Killingholme and Yarmouth.8 The Admiralty adopted Sueter’s scheme the following month and had most of the planned installations in operation prior to the outbreak of war. In response to the first successful U-boat attack on a British vessel, HMS Pathfinder, on September 2, 1914, the Navy beefed up the stations at Dundee and Killingholme. By the end of November the Navy implemented a revised plan specifically aimed at protecting the Straits of Dover, establishing bases to cover the fleet on both sides of the English Channel, in Dover, England, and on the French coast at Dunkirk. Earlier that same month the British introduced an offensive element to its air operations when a Royal Naval Air Service (RNAS) seaplane took off from Dunkirk to mount the first direct air strike on a German U-boat. Though the crew succeeded in locating the U-boat their attack failed when the submarine dived to escape. After this inauspicious beginning the Dunkirk crews devoted their attention mainly to reconnaissance and bombing of the German submarine bases at Zeebrugge and Ostend.

Lighter-than-air vehicles also played a role from the beginning of British anti-submarine operations. Gas-filled airships operating over the water offered the same endurance advantage that observation balloons held in land battles allowing aircrews to remain over their patrol areas hours longer than airplanes. By the summer of 1914 the Admiralty had taken over complete control of airship development excluding the Army, and in February 1915 Sir John Fisher, the First Sea Lord, ordered the construction of the SS (Submarine Scout) airship, the first lighter-than-air type specifically dedicated to anti-submarine warfare. The Admiralty’s goal in ordering SS airships focused especially on keeping open the Straits of Dover and access to the Irish Sea. Their apprehension proved well founded. By the spring, U-boats of the Deutsche Kriegsmarine (German War Navy) appeared for the first time off the west coast of Great Britain threatening receipt of western hemisphere imports. To offer political cover for its submarine campaign, Germany declared the waters around the British Isles a war zone, seeking to prohibit the area to any and all traffic, even ships representing neutral nations. Locating submarines in time to launch preemptive attacks required more speed and broader range than two-dimensional warfare offered, making aircraft crucial to defense. Submarines might be spotted cruising on the surface—time on the surface being necessary to recharge the U-boat’s batteries—or, in clear weather and calm seas, the boat might be visible even while submerged. By the end of the year, British constructors had built twenty-nine Submarine Scouts.

The amplified threat and the shift from two- to three-dimensional warfare required a broad reorganization of the entire naval defense system in order to incorporate the aerial component. As the war neared its first anniversary, RAdm. Sydney Freemantle, head of the Admiralty’s Signals Committee, categorized reconnaissance as the airship’s primary function, adding that its “duties are to locate enemy submarines and to keep them in sight as long as possible.” Successful communications between the airships and the Navy’s destroyers were clearly essential; to guarantee the strength of that link the Admiralty established special transmission and reception stations and proposed instituting a dedicated radio wavelength. The British Coast Guard administered the wireless stations reporting to each area’s senior naval officer or the Naval Centre. In August, in order to achieve tighter liaison between aircraft observers and the surface vessels whose attacks they would facilitate, the Admiralty removed all naval air stations from operational control of the director of the Air Department and placed them under the command of the various district senior naval officers.

During 1915, the RNAS concentrated on lighter-than-air craft for anti-submarine warfare owing to the “unseaworthiness of seaplanes and the general lack of heavier-than-air equipment and personnel.” Most of the airplanes and aircrew still in England remained unavailable for anti-submarine work, reserved instead for Royal Flying Corps training facilities. Those not tied up with training duties the RFC saved for home defense missions, thus protecting a nervous British public against the threat of zeppelin attacks on military targets and cities in the British interior. This allocation of resources reflected a new strategic approach to the defense of the British homeland. During the first months of the conflict responsibility for aerial defense of the United Kingdom had rested entirely with the Admiralty. In June 1915, acting on the recommendation of War Office Director of Home Defence Gen. Launcelot E. Kiggell, the chief of the Imperial General Staff divided control of home defense responsibilities. The Royal Naval Air Service stood accountable for attackers as they crossed the English Channel, and the Army’s Royal Flying Corps took charge once raiders had penetrated the coastline. Though shedding accountability for aerial defense of the mainland should have made more naval aircraft available for the war against the U-boats, division of control between the Army and the Admiralty and the transfer of naval air station command out of the Air Department to senior naval officers later in the summer instead exacerbated competition for these resources. The situation became further complicated by an increase in reconnaissance work over the English Channel and the North Sea that prompted the British to expand their Dunkirk Air Command. During the spring of 1916 the RNAS divided the command “into three wings, one for aerial reconnaissance, photography and control of naval gunfire, one for bombing and one for aerial fighting.”

Provision of bombing and aerial combat capabilities ensured that British naval aviators did not have to rely solely on passive defensive measures to combat the submarine menace. The highly mobile nature of the war at sea meant that naval aviators did not always have time to return to base or signal for help before their target disappeared. The Dunkirk group had already demonstrated the potential value of direct interdiction by launching some of the first aircraft attacks on U-boats at sea. Early in the war the Royal Naval Air Service organized an offensive capability, hoping to hit the enemy in his lair rather than simply waiting for his ships to appear. In its first month of operations, March 1915, Dunkirk crews launched bombing attacks on Ostend, Middlekerke and Hoboken, Antwerp, claiming (inaccurately, as it turned out) one submarine destroyed and two damaged. The naval airmen organized a combined air- and seaplane force some thirty strong utilizing seaplane stations on England’s east coast and a newly developed seaplane carrier, HMS Empress, with the aim of attacking German submarine pens across the English Channel. The group carried out several missions, but did not achieve significant success.

By the end of 1915 improved German antiaircraft defenses and the relative ineffectiveness of the light bomb loads early air- and seaplanes could carry caused the RNAS to forego further heavier-than-air offensive activity. Initially, airships appeared to offer an alternative, given their more impressive carrying capacity, but ultimately lighter-than-air bombers proved no more successful in achieving measurable submarine destruction than their heavier-than-air counterparts. Consequently, British airship crews returned to concentrating on reconnaissance, searching for submarines already at sea in conjunction with surface vessels rather than attacking the U-boats in their pens.

Despite the considerable attention historians have devoted to its bombing attacks on London throughout the war, the German Naval Airship Division devoted substantially more of its resources to reconnaissance than to destruction. Of the 1,497 sorties German airship crews mounted during the conflict, 971 (65 percent) had scouting over the North Sea as their purpose, compared to the 306 missions (20 percent) flown to drop bombs on England. The rather meager £1,527,544 total damage done to England during the German airship raids offers clear evidence that airship crews flying reconnaissance missions performed potentially far more valuable services.

Throughout 1916 and into the following year the British developed the Coastal airship, a larger design capable of longer patrols, and added to the number of stations dotting the United Kingdom’s shoreline. Between January and December, the RNAS constructed new facilities at Pembroke, Pulham, Longside, Howden, Mullion, and East Fortune, and opened an airship school at Cranwell. Reconsidering its earlier decision to abandon efforts to copy Germany’s successful zeppelins, the Navy resumed construction of a project previously cancelled, Rigid Airship No. 9, and built a large storage shed to accommodate the aerial behemoth at Howden. Anticipating further additions to its rigid aerial fleet in 1917, the Admiralty built more sheds at its Pulham, Longside, and East Fortune stations, and at the Cranwell training facility. Extending its reach off the British mainland the RNAS added an SS station at Caldale, in the Orkney Islands, for work with the Grand Fleet at Scapa Flow.

Despite these preparations and its early appreciation of aviation’s potential value in the anti-submarine war, not until the third year of the war did the Royal Navy give priority to the design and construction of heavier-than-air aircraft capable of directly attacking the U-boats. Until then neither the British nor the French felt any pressing need to rush. Germany’s desire to keep the United States out of the war had led the Kaiser to restrict the conduct of his U-boat commanders. This political strategy prevented submarines from achieving their full destructive potential and kept Allied naval losses within manageable limits during the war’s first two years. But by the second half of 1916 the German military and political situation had both eroded. Germany’s attempt to defeat the French at Verdun had failed, ending in nearly as many German casualties as French, a situation made worse by hundreds of thousands further German, French, and British losses at the battle of the Somme. In the wake of these setbacks, the Kaiser’s high command reorganized its military, naval, and aviation assets hoping that, by bold measures, they might defeat the French and British in whatever time remained before the United States entered the war. As a key component of this new strategy, the imperial government stepped up U-boat activity permitting the Kriegsmarine to return to unrestricted submarine warfare.

The lull in submarine activity in the Atlantic during the first half of 1916 had been prompted largely by American diplomatic protests. Germany’s failure to bring about a favorable resolution to the war at Verdun and the heavy fighting at the Somme brought home the prospects of eventual defeat. Balanced against the possibility of losing the war the political risk of offending the United States seemed one worth taking. U-boats resumed hunting prey in British home waters in August 1916 and the new threat prompted the British to expand seaplane patrols in September. In response, Adm. Stanley Cecil Colville, commander of the Royal Navy at Portsmouth, requested installation of a four-machine seaplane base at Portland to supplement the existing facility at Calshot and two more SS stations, one for the Isle of Wight and one for Portland, each with ten airships.

Actions like Colville’s proved preliminary to a wholesale reorganization of the war against the U-boat and, on December 18, 1916, the Admiralty created the Anti-Submarine Division (ASD). The new organization took a special interest in aviation and vastly expanded both the number of heavier- and lighter-than-air craft available and the role of its aerial assets in the anti-submarine campaign. Creation of the Anti-Submarine Division centralized naval aerial activities that previously had been left to the individual prerogatives of each region’s senior naval officer. The new division organized a coordinated system of coastal patrols and split naval aviation according to its offensive and defensive functions, much as the Dover Command had earlier divided its organization into reconnaissance, bombing, and fighting wings. Offensive assets included the airplanes and seaplanes patrolling Britain’s waters actively hunting submarines, purely defensive reconnaissance missions being left to airships due to their endurance. Given these measures made areas near the coasts safer but left ships farther out to sea to their own devices, the director of the ASD further recommended enhancing direct protection of the fleet by equipping British vessels with kite balloons to improve their fields of vision.

By January 1917 the British had built a massive naval aviation program that combined three seaplane carriers in service with more under construction, ships equipped with kite balloons, plans for rigid airships, coastal airships protecting the home waters, and large seaplanes able to patrol farther away. Yet, despite this abundance of assets, Adm. Sir David Beatty, commander-in-chief of the Grand Fleet, regarded his air strength insufficient compared with his needs and recommended to the Admiralty that: “all naval officers who are engaged upon duties not connected with the fleet should be withdrawn and utilized for developing the Royal Naval Air Service.”

The early months of 1917 also saw Germany remove all remaining restraints from its U-boat commanders, resuming unrestricted submarine warfare that the German High Command hoped would bring the war to a successful conclusion within six months.40 Instead, within just over two months the decision to escalate its cruiser war produced the outcome Germany most hoped to avoid. On April 6, 1917, the United States declared war on Germany. Ultimately, the resumption of unrestricted attacks combined with a botched German attempt to recruit Mexico into the war on its side, prompted the United States to enter the conflict.

The U-boat war reached its peak coincident with the American entry into the war. The last half of April 1917 saw approximately 50 percent of the German submarine fleet at sea with five ships sunk on average each day. The 19th proved the worst single day of the month for the Allied merchant fleet, when U-boats and German mines sunk eleven ships and eight fishing vessels.42 This spike in submarine activity pushed the average for the year 1917 to three ships sunk per day. As part of the British response the RNAS laid out formal areas for aerial patrols and categorized those missions as “routine,” “emergency,” and “contact,” with contact flights reserved for its seaplanes. Beginning operations in late April, the new patrol system received formal Admiralty sanction on May 8, 1917. Station commanders at Nore, Harwich, Yarmouth, Killingholme, South Shields, Dundee, and Houton Bay coordinated patrol hours and areas in systematic fashion to avoid overlap and to ensure that each district had at least one aircraft on duty in the air during all possible flight hours.

The British further refined their naval aerial reconnaissance system in the spring of 1917 designing both the spider web system and Tracing U. The spider web created an imaginary octagon of chords radiating 60 miles out of the North Hinder light ship in the English Channel, an epicenter around which seaplanes could systematically patrol guaranteeing maximum coverage with a minimum supply of aircraft. Spider web patrols began on April 13, 1917, and in the first eighteen days five flying boats flew twenty-seven patrols sighting eight U-boats and bombing three. Tracing U (“U” for U-boat) divided the southern portion of the North Sea into grids similar to those in common use by artillery units operating on the Western Front, allowing commanders of coastal air stations to quickly pinpoint submarine sightings, then dispatch attacking aircraft or communicate the information to nearby destroyers.

Organizational refinements to the reconnaissance and patrol system proved effective and valuable, but the adoption of the convoy system in late April 1917 proved the most significant move forward toward defeating the submarine. To this point in the war many senior commanders in the British Admiralty opposed convoying merchant vessels believing that warships should be reserved for offensive action rather than escort duty. The large increase in sinkings that followed Germany’s resumption of unrestricted submarine warfare in February, the success of an experiment in protecting French coal vessels begun the same month, and the entry of the United States into the war in April combined to reverse their opinions. Furthermore, America’s enlistment in the Allied cause increased the number of ships available for convoy duty and opened US ports for use as convoy assembly points.

The added naval capacity brought with it greater responsibility for Allied aviators. In order to protect the Atlantic courses over which the American Expeditionary Force and its equipment would travel naval aviation expanded its former role in protecting Anglo-French military traffic and neutral merchant shipping during the last half of 1917. Land-based airplanes and seaplanes could patrol the areas off the British and French coasts to the extent of their range covering the arrival of ships during the last leg of their travel from the United States. Kite balloons towed by warships could extend the effective field of vision of the convoy before the aerial escort picked it up, allowing crews a lifesaving early look at potential attackers throughout the journey. The British strengthened the new system further by completing construction of the network of airship stations the RNAS had begun organizing in 1916, the last becoming fully operational by the end of 1917. The RNAS, of course, protected the British coast and that portion of the French shoreline most vital to arriving British traffic. The French Navy also vigorously defended its own ports, but paid more attention to the Mediterranean and the Adriatic, leaving the Atlantic largely to their British allies and later to the AEF. The US Navy joined the effort within a few months of the American declaration of war and throughout 1918 expanded the network of protective air stations further still, taking over some British, French, and Italian coastal bases and constructing some of its own.

After the task of organizing an American army, an army that barely existed when the United States declared war, protection of that force as it crossed the Atlantic to fight on the Western Front represented the most important job facing American military and naval leaders in April 1917. In addition to the naval air stations they would build or take over in Europe, US Navy commanders faced the challenge of defending embarkation and receiving bases on their own side of the Atlantic, as well as a small number of less vulnerable installations on the Pacific coast. Even with aerial patrols fully operational the Navy would have to defend its ships against German submarines through most of the Atlantic crossing without the direct assistance of airplanes owing to the limited range of aircraft operating out of its coastal air stations. Taking their cue from British and French experience, American naval commanders enhanced the safety of the US fleet during that vulnerable period by equipping nearly every class of its ships with balloons to provide cover for the convoys.

Building the aerial organization necessary to protect the fleet required putting US naval aviators on duty in France as quickly as possible. Within five weeks of the American declaration of war the Navy dispatched Lt. Kenneth Whiting to take charge of the first group of naval flight trainees sent to France. Training preparations progressed well enough that by July the Navy reported to the French that two schools had been established within the French interior, one at Tours to instruct pilots and the second at San Raphael for prospective mechanics and observers. Plans had also been made for an additional school to teach naval artillery observation as well as an operational station at Moutchic-Lacanau.

Once trained the Navy’s aviators would serve at a network of stations in the planning stages or already under construction on both sides of the Atlantic. By July 1917 provisional plans existed for the organization of naval air stations at Dunkerque, Le Croisic, and St. Trojan in addition to the facilities at Tours, San Raphael and Moutchic-Lacanau. Operations commenced at Moutchic-Lacanau on November 11, 1917 and within a week the naval air station at Le Croisic launched the first of an eventual 1,045 wartime patrol flights.

By the following April another four stations had opened in Great Britain and France, at Killingholme, Ile Tudy, Dunkerque, and Paimboeuf, as well as a base at Bolsena, Italy. Patrols from these and the extant British and French air bases impressively demonstrated the value of aerial reconnaissance to the convoy system. In the spring, RAdm. Henry G. Wilson told the French press that cooperation between the French and US navies had substantially reduced sinkings in the waters along the French coast, comparing October 1917, during which thirty-four ships were torpedoed to February and April 1918, when no ships had been lost to the U-boats.

Though submarine losses directly attributable to aircraft action are difficult to document, the mere presence of airplanes or airships frequently played critical roles in the demise of U-boats. Two incidents, both of which coincidentally took place on April 24, 1918, provide typical examples. In the first, airship SSZ 41, stationed at RAF Polegate received a report of a submarine operating southeast of the Isle of Wight. In response, the crew patrolled in the vicinity of the submarine’s reported sighting for twelve hours in a dense fog, returning without having sighted the U-boat. A torpedo boat destroyer found and sank the German raider later in the morning. Official speculation held that the submarine had been forced to remain submerged in order to avoid detection by the airship and that by morning the desperate need for fresh air and recharged batteries forced the boat to the surface, putting it in a situation where it could no longer avoid detection.

The second incident further demonstrates the potential of air-sea cooperation. Two American seaplanes patrolling off the French coast near Penmarch spotted what they believed to be a German submarine operating two miles from a convoy, responding to the opportunity with two bombs. Tracking the encounter, USS Stewart left its position in the convoy to investigate. While en route, the Stewart watched the aircraft mark the site with smoke bombs and, on arriving at the scene the American ship dropped depth charges after which the crew observed oil on the surface. Though no wreckage surfaced, other ships in the vicinity observed oil as late as two days later, providing strong evidence of a sinking.

The success of the patrols and the convoy system firmly established what the world’s navies had been learning throughout the war—that extending the vision of ships using aerial observers saved lives and material. Over the course of the war’s remaining months the US Navy established a dozen stateside naval air bases, in addition to a pair in Canada, one each in the Azores and the Panama Canal Zone, and a total of twenty-seven air stations in Europe. The stations on the American side of the Atlantic functioned primarily as coastal patrol stations protecting the convoy assembly points from the threat of German submarines. The nineteen naval air stations on the European side of the Atlantic that conducted similar reconnaissance flights generally communicated their sightings to nearby ships but occasionally launched their own attacks on real or suspected submarines.

Considering naval heavier- and lighter-than-air units along with the Army’s airplanes and balloon sections makes it clear that American aviation had reconnaissance and observation as its main purpose. Fifteen North American naval air stations and one in the Panama Canal Zone had reconnaissance as their primary duty, as did nineteen of the US Navy’s twenty-seven European stations. In comparison, the French established a total of thirty-six coastal seaplane bases, as well as a half dozen balloon centers, and four dirigible bases. Adding those thirty-five American bases to the forty-five US Air Service airplane squadrons and the seventeen American balloon companies working on the Western Front raises the total number of American aviation units that served during the conflict to ninety-seven, out of which seventy, or 72 percent, performed reconnaissance or observation as their primary function. Regardless of how military and naval air power developed over the rest of the twentieth century, during the First World War its principal and most valuable function lay in the aviators’ ability to see and report what happened on the ground and water.

The numbers of aircraft acquired by the world’s navies during the war further document the growing appreciation for aviation. The British Navy increased its heavier-than-air aircraft stock from fewer than one hundred to nearly three thousand, its airship strength from six to 111, and its inventory of captive balloons from two to 200. The Deutsch Kriegsmarine air fleet grew from twenty-four air- and seaplanes to nearly 1,500, and its lighter-than-air division worked its way through eighty-three airships, beginning the war with one and making it to the armistice with nineteen. The French Navy enlarged its heavier-than-air aircraft supplies from eight at the outset of war to 1,264 at the end, alongside fifty-eight airships and 198 kite balloons. Even the more limited resources of Austria-Hungary and Italy grew exponentially, the Austro-Hungarian air- and seaplane fleet expanding between eleven- and twelve-fold and the Italian inventory by more than twenty-fold. For its part, over the relatively short time it spent at war the US Navy grew its aircraft inventory from fifty-four airplanes and seaplanes, one airship, and two balloons in April 1917 to over 2,100 heavier-than-aircraft, fifteen airships, and more than two hundred balloons at the armistice. These figures reflect the same kind of progress the world’s other warring powers made during the conflict.

Although these dramatic operational changes and numerical increases speak to how thoroughly aviation had been accepted into the world’s navies, they do not begin to hint at the change in character the presence of aircraft brought to the war at sea. Although aircraft may have failed to live up to naval leaders’ prewar expectations due to airframe and powerplant technological limitations, through its reconnaissance function naval aviation prevented many potential sea disasters. History’s failure to acknowledge this enormous contribution lies in the challenge proving a negative always presents to the post-event analyst. In evaluating the impact of the RNAS/RFC merger that created the Royal Air Force on April 1, 1918, one historian argued the demise of the Royal Naval Air Service “crippled Britain’s credibility as a sea power.” During the First World War and afterwards the US Navy arrived at the same conclusion. The day had arrived when a modern navy seeking to project its nation’s power around the globe could not hope to compete without its aircraft.