page_title: Drop tank
section_title: Paper-based drop tanks
hierarchical_section_title: Drop tank / History / Paper-based drop tanks
caption_attribution_description: English: Jettison Petrol Tanks- the Production of Jettison Tanks For USE by the United States Army Air Force and Royal Air Force, Britain, 1944 At a factory producing jettison petrol tanks for the American and Royal air forces, somewhere in Britain, Miss Ethel Prett (left) and Miss Nellie Robery work at a large press which forces the two spigotted ends onto the body of the tank. Behind them, a large stack of tanks can be seen.
context_page_description: In aviation, a drop tank is used to describe auxiliary fuel tanks externally carried by aircraft. A drop tank is expendable and often jettisonable. External tanks are commonplace on modern military aircraft and occasionally found in civilian ones, although the latter are less likely to be discarded except in the event of emergency.
context_section_description: Faced by wartime metal shortages and a need to extend the range of fighter craft, the British came up with drop tanks made of glue-impregnated kraft paper, which had excellent tolerance characteristics for extreme heat and cold necessary for operation on an aircraft as well as being waterproof.
  Since the glue would slowly dissolve from the solvent effects of the fuel (sometimes developing leaks within a few hours of being loaded with fuel) these were strictly a single-use item, used in typically chilly Northern European conditions, filled immediately before take off, jettisoned in the event of an aborted mission and only being required for the outbound portion of any flight.
  Such papier-mâché tanks were assembled from three main components, the nose cone, tail cone and the body, each shaped over wooden forms, the centre section created by wrapping layers of the impregnated paper around a cylinder, the end caps hand-laminated with petal-shaped pieces sometimes named gores.
  Before final assembly wooden anti-slosh baffles were installed, pipes and fittings were attached and the interiors coated with fuel-resistant lacquer and the three pieces were bonded together in press. Once the tank had cured, it was pressure tested to 41 kilopascals (6 psi) and passing tanks were given two coats of cellulose dope followed by two coats of aluminium paint. (British paper drop tanks can be distinguished from outwardly similar metal tanks by colour, paper tanks were silver in appearance, while metal tanks were grey.)
  Some 13,000 papier-mâché tanks were made and used by the RAF, the vast majority used in the course of the war, conserving a considerable amount of metal. Very few examples survive due to their expendable nature and low intrinsic value at the time of their creation, and the fact that they are not inherently robust. While probably a nuisance for those under the flight path when the empty tanks were released, as they were lightweight and comparatively fragile it is unlikely to cause anything but anxiety, the Germans authorities going so far as to distribute leaflets, explaining that drop tanks are not bombs.
  U.S. paper tanks were developed by Col. Bob Shafer and Col. Cass Hough, who spent many hours developing a 110-gallon (416 litre) paper tank, then getting them into series production at Bowater-Lloyd's of London, only to be told by experts at Wright Field "paper tanks are absolutely unfeasible and will not do the job for which they are intended". Since by the time the experts made that pronouncement 8th Air Force fighters had already used more than 15,000 paper tanks without a failure, the criticism was not taken seriously.
  However it may explain why the most often-used fuel tanks for single-engined American fighters operating in Northern Europe were the 75-gallon (284 litre) capacity all-metal tank (made from two halves of formed aluminium with a prominent horizontal seam running along the tank's midline). Another common metal drop tank was the 150-to-165-gallon model used by P-51s, P-47s and P-38s.
caption: 110 US-gallon (416 litre) paper drop tanks, destined for USAAF and RAF use, being manufactured at a British factory (1944)
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