The Aircraft Operated from Submarines in World War I

The Friedrichshafen FF29 on the bow of U-12
(from the War Relics Forum)

 While the combat pinnacle of aircraft-carrying submarines is considered by many to be the big Japanese I-400 class boats of the Second World War that could carry three Aichi Seiran floatplanes, the roots of operating aircraft from submarines has more humble beginnings in the First World War based on the personal initiative of a U-boat captain, Oberleutnant Freidrich von Arnauld de la Periere who was the base commander for the submarine base at Zeebrugge in occupied Belgium. Quite unusually for a submarine officer, he was also an aviator which gave him unique insights into the potential for aircraft that many of his other naval comrades did not possess. Working with a friend who also happened to be a U-boat captain of the submarine U-12, Walther Forstmann, they hatched an plan to launch floatplanes off the foredeck of the submarine to attack British targets. At the time, the only way to attack British targets was either via Zeppelin airship or large bombers like the Gotha G.V. In the last few weeks of 1914, the Germans did try to attack British targets with floatplanes based across the Channel but were largely unsuccessful as the range needed resulted in a very small bomb-load. The first confirmed attack on a British target, in fact, was by Friedrichshafen FF29 floatplane on 21 December 1914 that dropped two bombs and missed against a pier in Dover. 

The two men came from illustrious backgrounds- von Arnauld de la Periere's brother, Lothar, was the most decorated U-boat captain of the First World War and with 194 ships sunk, the most successful submarine captain in history. Walther Forstmann was the second most decorated U-boat captain of the First World War and with a 146 ships sunk, he was the second most successful submarine captain in history after de la Periere. Realizing that there were few Zeppelins and Gotha bombers to prosecute a large scale attack on British targets, the two men surmised that floatplanes with their limited radius when flying from the Continent might have a more utility if launched from the decks of U-boats that could approach more closely to their intended targets. With single engine floatplanes more widely available, they set out to try and prove the concept starting on 6 January 1915 with a Friedrichshafen FF29 floatplane lashed to the foredeck of U-12 to carry out sea trials. Within the Zeebrugge harbor, they had determine that the submarine would have to trim down at the bow with the FF29 floating off and then taking off from the sea. On their first operational mission, with Forstmann captaining U-12 and de la Periere flying the FF29 with an observer, they approached within thirty miles of the British coast when the FF29 was floated off to begin a reconnaissance mission. They flew along the coast undetected, but were unable to rendezvous with U-12 due to deteriorating weather and returned to Zeebrugge instead. 

Emboldened by their success, de la Periere and Forstmann had the FF29 modified with bomb racks to carry 12 kilogram bombs. They determined that calmer sea states were needed to not only allow the FF29 to take off, but to prevent damage to the floatplane as it was lashed to the U-boat's foredeck. Over the course of the year in 1915, the "Zeebrugge Fliers" flew twenty-six raids from U-boats against British and French coastal targets. On Christmas Day 1915, he managed to fly up the Thames Estuary and drop two bombs on London which did little damage. He successfully exited the area to safety despite being chased by three fighter aircraft. This all took place without any sanction or support of the German high command- as the FF29s were light floatplanes, de la Periere and his other pilots he trained often found their biggest issue wasn't British defense but numerous technical issues with the aircraft being subjected to such harsh use. But morale was high amongst the pilots and the U-boat crews- given that the U-boat was a relatively new weapon of war at the time, the crews took special interest in the pilots who were trying a relatively new weapon as well in the same hazardous sea environment. A formal report of their efforts was submitted up the chain of command, but they were told explicitly to stop their efforts. In the words of the German high command, "U-boats operate in the sea, aircraft operate in the air. There is no connection between the two."

Sopwith Schneider floatplanes on the aft deck of the sub E22
(from @RNSubMuseum's Twitter stream)

Across the English Channel, the British were also giving consideration to operating aircraft off submarines, but for a defensive role instead of an offensive role. Germany had opened up a new phase in the war with its strategic bombing campaign against British targets using Zeppelins on 19-20 January 1915. The airships could carry a much more significant bomb-load than most aircraft in the German inventory and they were able to fly at a height that made interception by British fighters difficult. Both the Army and the Royal Navy each proposed their solutions to the "Zeppelin" problem, the Army suggesting fighters with better engines for higher altitude performance and larger caliber anti-aircraft cannon that could reach the airship's bombing altitudes. The Navy, however, came up with a unique solution with the observation that Zeppelins crossed the North Sea on their way to their targets at relatively low altitudes and then climbed to their bombing altitudes once reaching the coast. Although ships had been used to launch floatplanes against the Zeppelin bases in December 1915 in the first "carrier" attack, the Navy proposed the use of submarines which would be less visible to Zeppelin crews as they made their crossing at low altitudes. Such a submarine could launch aircraft that would have had an easier time intercepting the airships at the lower altitudes. Given authorization, the Royal Navy drydocked the 660-ton submarine E22 for the addition of two parallel ramps on the aft deck that extended from the conning tower to the end of the upper deck casing. 

On 24 April 1916, the newly-modified E22 docked at Felixstowe to take on two Sopwith Schneider floatplanes. The Schneider was the floatplane version of the Sopwith Tabloid fighter. The name came from the floatplane Tabloid being used in the 1914 Schneider Trophy race. The land-based Tabloid was used as a fast scout by the Royal Flying Corps (the RAF's predecessor). The E22 took the two aircraft lashed on its modified aft deck for sea trials in the Heligoland Bight, the area where Zeppelins often began their North Sea crossing towards their targets. The effort was near disastrous- the sea state was too rough for the Sopwith Schneiders which had their floats snapped by the waves. On the following day after it was decided to head back to the naval air station at Felixstowe for replacement aircraft, the E22 was torpedoed and sunk by U-18, ending any significant British experiments for the duration of the war. 

The Brandenburg W20 flying boat
(from Their Flying Machines)

Interestingly the two operations of the First World War involving the use of aircraft from submarines didn't involve the most obvious use- reconnaissance. The Germans used it for bombing raids and the British intended to use their aircraft for Zeppelin interception. That didn't stop some German engineers from considering the problems of operating aircraft from submarines. Ernst Heinkel before he would become famous had designed and built a flying boat, the Hansa-Brandenburg W20, designed from the outset to be operated from submarines. As the German naval command began work on larger submarines, Heinkel began work in 1917 on a compact single seat flying boat that could be folded up and stored inside a watertight compartment on a U-boat. Three aircraft were ordered with the prototype flying in the same year that Heinkel began work on the W20 design. A biplane design with a single pusher engine, the W20 was a bit of a weak performer with an 80 hp engine and it took fifteen minutes to climb to 3,000 feet. But the diminutive aircraft could be assembled and disassembled in three minutes and stored in a watertight compartment only 20 feet long and 6 feet in diameter. The design never went to sea trials aboard a U-boat as by late 1917, no spare subs could be afforded to Heinkel and the Hansa-Brandenburg team. 

The LFG Roland V19 "Putbus"
(from Google Snipview)

In 1918, the British returned to the idea of operating aircraft off submarines- only this time they used an SSZ (Sea Scout Zero) class blimp towed by a K-class submarine. It wasn't too successful as the SSZ blimps were too large and it hampered the mobility and flexibility of the submarine. Towed observer kites (large box kites carrying a single very brave observer) were also trialled, but they proved equally unsuccessful in trials as well. That same year, though, the Germans took one more shot at the submarine-compatible aircraft problem. The Luft Fahrzeug Gesselschaft (LFG) Roland company produced a single seat scout plane called the LFG V19 "Putbus". Unlike other aircraft trialed, the Putbus was a monoplane with twin floats with aluminum skin. Fuel was contained in the detachable wings which had shut off valves so the wings could be attached or removed without having to drain the fuel tanks. In flight tests the Putbus could fly up to 112 mph, much faster than any other aircraft flown off submarines thus far and appeared to be quite superior to the Hansa-Brandenburg W20. However, while the W20 could be readied for flight or stowed in as little as three minutes and used a single 20x6 foot compartment, the Putbus took at least thirty minutes for assembly for flight or stowage and required five compartments to stow its components aboard a U-boat. Needless to say, the German naval command was less than enthused but by the time it came to take the Putbus to sea, the war had ended. 

Source: Strike From Beneath the Sea: A History of Aircraft-Carrying Submarines by Terry C. Treadwell. The History Press, 2009, pp 13-24.