William T Althoff, Forgotten Weapon: U. S. Navy Airships and the U-boat War. Annapolis: Naval Institute Press, 2009. 417 pp. heavily illustrated with B& W photographs; maps, chronology, glossary, appendixes, bibliography, notes, index.

Review by Andrew Lambert
King’s College London.

Long recognised as the expert on United States Navy lighter than air (LTA) operations William Althoff has once again mined his seminal 1990 text Sky Ships: A History of the Airship in the United States Navy for a theme that required further development. This study shifts the focus from the broad focus to the wartime role of small non-rigid ‘blimps’ in the context of the anti-submarine campaign. Despite the abandonment of the large rigid airships, after the costly failure of successive American built ships, and the death of their chief proponent, Admiral William Moffett, lighter would not die. Instead it was stripped back to the training cadre of blimps at Lakehurst New Jersey. As the world spiralled down towards a Second World War the LTA programme managed to cling onto the coat tails of a vast expansion of American naval power, one that generated a force of over 7,000 officers and men, one that would put over 100 blimps into the sky between the Canadian frontier and Brazil, with detachments operating from Morocco, France and Italy. Some of the LTA leadership, notably career LTA aviator the abrasive Admiral Charles Rosendale, hoped to rebuild the rigid airship programme on the back of a successful war, pushing designs for long range LTA aircraft carriers with seven scout bombers, or massive strategic transports. Instead the service received over 100 K type combat blimps, and a useful force of training ships, all produced by the Goodyear Corporation. Goodyear had made a long term commitment to the technology, operating the world’s only truly commercial LTA fleet.

It might be wondered what role the small non-rigid airship could fulfil in 1940 that would justify the expenditure of considerable money, industrial effort and manpower. There were many critics at the time, and the consensus down to the present has been that more aircraft and/or surface ships would have been a better choice. Althoff makes a good case for LTA, and may just prompt a revision of those judgements. By addressing the U-boat war at all levels, from grand strategy to tactics his book places the LTA effort in a clear context. The Navy had an LTA capability, and simple blimps had been a critical convoy escort asset for the British in 1918, when they deterred U-boat attacks, reported on their movements and generally denied them the opportunity to operate on the surface. When the United States joined the Second World War a dramatic U-boat offensive struck the Eastern Seaboard, exposing an almost catastrophic failure by state and service to anticipate and prepare. Everything that could fly was dragged into the defence of shipping. The blimp worked because it faced no air threat on the American coast, could stay aloft for 12 to 18 hours, was highly visible, provided an excellent viewing platform and operated at low speeds that were suitable for the escort role. In early 1942 blimps rushed into service to provide a modicum of protection to coastal shipping, and they did so without effective weapons or sensors. Despite these limitations their presence provided useful area denial and a potent deterrent, one that helped to turn the tide. When the U-boats withdrew to the West Indies, Venezuela and the Panama Canal Zone the blimps followed them, with major infrastructure projects needed to create the big sheds, aprons and helium refinement plants that were required to sustain the gasbags. Fields in Trinidad and then along the Brazilian coast supported squadrons that escorted high value convoys of oil and bauxite.

At 75 mph flat out blimps were too slow to press home an attack on a diving submarine, and vulnerable to anti-aircraft fire so standard ASW procedure for blimps was to report sightings and then tail them from a safe distance by eye, radar or latterly MAD (Magnetic Anomaly Detection), calling up surface and heavier than air support. The only blimp to exchange fire with a U-boat, K74, spotted U134 off Florida, and the skipper chose to engage, dropping depth charges and firing the single 50 calibre machine gun. With the envelope punctured by 20mm fire the blimp went down, although the crew were rescued. The U-boat suffered significant damage to her dive tanks, aborted her mission, and was sunk by British aircraft as she neared base in France.

A squadron deployed to Morocco conducted night ASW with MAD in the Straits of Gibraltar, in mid-1944, before the blimps were sent to the south of France, Tunisia and Italy where they spotted minefields and directed the surface minesweeping effort with great success. This was another role pioneered by the Royal Navy in 1918, in which LTA was far superior to HTA. The Pacific theatre witnessed a few tentative early ASW patrols, but by the time the blimps were combat ready the Japanese submarine threat had disappeared and the blimps were never deployed to the combat zone, despite successful carrier compatibility exercises.

In August 1943 LTA found itself in the middle of a bitter turf war between the Army Air Force and Navy for control of land based air ASW. The programme was stopped; orders for new airships were cut back, ending production of the new, larger M type at 4 units, and the K series at 135, with spares and 22 training ships. By this stage the blimp was finally getting effective sensors, and the hint of useful weapon. After extensive trials on blimps and aircraft MAD, produced traces that would allow a blimp to follow a submerged U-boat, and plan an attack. By 1944 the doctrine was to locate U-boats by eye, or by radar, and then track them underwater with MAD, to deliver the contact up to more effective killer systems. The addition of sono-bouys, another system developed for the blimp, finally linked all the pieces of the system into a usable platform, about two years after it would have been really useful, against the first U-boat campaign off the East Coast. By late 1944 the development of the modern diesel electric submarine had fundamentally changed the balance of power between air and submarine. This gave the MAD equipped blimp a key role, detecting and especially tracking an underwater target capable of 16 knots. Plans to base a squadron in the United Kingdom to meet this emerging threat were aborted by the end of the war, with two ships already in the Azores. Using blimps for inshore work would free up very long range HTA for distant operations.

In late 1944 the blimps also began to be fitted with acoustic homing torpedoes, the ideal attack weapon for the platform. In April 1945 K72 dropped an acoustic, and the accompanying destroyer escort picked up a clear underwater explosion, probably the destruction of U879. However, in the absence of debris and wreckage the kill was never awarded. Another blimp joined in the last American U-boat kill, too little and too late to hit the headlines.

The 1943 cutbacks hit LTA development, but the killer blows were the high casualty rate from basic aviation accidents, and the failure to score a single clear cut U-boat kill. While Althoff stresses the negative aspects of the Navy’s handling of LTA in the wrap up chapters 8 and 9, the programme was a success. LTA retained key personnel and survived the war, acquired new N type ASW blimps, proof positive that the Navy valued LTA in the jet age, and even took on a new role in national defence, providing long endurance Airborne Early Warning. In fact the Navy carried on with LTA, a decade after it paid off the last battleship. Given the utter lack of interest in LTA in any other Navy this suggests that US Navy LTA was pushed to its limits by a small but determined and pugnacious band of believers, led by Admiral Charles Rosendale, and their long term allies at the Goodyear Corporation. The blimps helped to drive the U-boats out of American and Caribbean waters, a result that should have satisfied even their harshest critics, and released other air ASW assets for operations further afield. As convoy escorts they deterred and diverted U-boats, saving countless ships and men; indeed Althoff notes that only one merchant vessel was sunk while under blimp escort. By 1945 they had the technology to be serious U-boat killers, but ran out of time to prove the point.

Althoff’s expertise, insight and enthusiasm shine through this excellent book, both as a record of a genuinely under-appreciated weapon system, and another case study of the technological innovation in wartime. The blimp may have lacked the allure of the big rigid ships, but it was a far more effective weapon in the war that was fought between 1941 and 1945. This elegant and effective book provides a lasting monument to the achievement of the LTA squadrons, establishing their contribution to victory beyond any doubt. Now we must hope that the author is ready to finish the story, treating the post-1945 LTA effort in similar fashion.

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