page_title: Drop tank
section_title: History
hierarchical_section_title: Drop tank / History
caption_attribution_description: English: P-51D-5NA Mustang 44-13357; Lt Vernon Richards, Tika IV 8th AF / 374th FG / 361s t FG. Was later assigned to Lt. Alfred B Cook Jr who renamed it Sailor Girl Shirl - KIA 16 Nov 44 - crashed near Little Walden.
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: The drop tank was used during the Spanish Civil War to allow fighter aircraft to carry additional fuel for long-range escort flights without requiring a dramatically larger, heavier, less maneuverable fuselage.  During World War II, the German Luftwaffe began using external fuel tanks with the introduction of a 300-liter (80 US gallon) light alloy model for the Ju 87R, a long-range version of the Stuka dive bomber, in early 1940. The Messerschmitt Bf 109 fighter also used this type of drop tank, starting with the Bf 109E-7 variant introduced in August 1940. Fitted also to the Focke-Wulf Fw 190, the 300 liter tank, available in at least four differing construction formats — including at least one impregnated paper material, single-use version — and varying only slightly in appearance, became the standard volume for most subsequent drop tanks in Luftwaffe service, with a rarely used 900 litre (238 U.S. gallon), fin-stabilized large capacity drop tank used with some marks of the Messerschmitt Bf 110 heavy fighter and other twin-engined Luftwaffe combat aircraft.
  The first drop tanks were designed to be discarded when empty or in the event of combat or emergency in order to reduce drag, weight, and to increase maneuverability. Modern external tanks may be retained in combat, to be dropped in an emergency.
  The Allies commonly used them to allow fighters increased range and patrol time over continental Europe. The RAF used such external fuel tanks in 1942, during the transit of Supermarine Spitfires to Malta.
  The Imperial Japanese navy design specification for what came to be the Japanese Mitsubishi A6M Zero fighter included endurance with drop tanks of two hours at full power, or six to eight hours at cruising speed. Drop tanks were commonly used with the Zero, even on Combat Air Patrol (CAP). The Zero entered service in 1940.
  Bomber theorists insisted formations of heavy bombers with elaborate defensive armaments would be self-defending, believing long-range escort fighters to be "a myth" as they could be easily forced to drop the tanks by minor harassment at the beginning of the raid being more concerned that long-range medium bombers might compete for resources and so compromise their goal of creating vast fleets of heavy bombers. In the face of such entrenched attitudes in 1941 airmen such as Benjamin S. Kelsey and Oliver P. Echols worked quietly to get drop tank technology added to American fighters such as the Lockheed P-38 Lightning.
  It was only with drop tanks supplying 450 US gallons (1,700 l; 370 imp gal) of extra fuel per fighter that P-38s could carry out Operation Vengeance, the downing of Admiral Isoroku Yamamoto's airplane. (For this mission, each fighter carried one drop tank of approximately 150 to 165 US gal (570 to 620 L), and a larger one of approximately 300 to 330 US gal (1,100 to 1,200 L).
  Even after such experience showed the necessity for drop tanks, inflexible thinkers such as 8th Air Force General Ira C. Eaker had to be transferred out of commanding positions (and replaced with Maj. Gen. Jimmy Doolittle) so that drop tanks and range extension plans could be widely implemented in 1944 for American escort fighters.
  External drop tanks turned the Republic P-47 Thunderbolt from a short-range interceptor aircraft into a long-range escort and air superiority fighter, enabling it to accompany bombers from British Isles into Germany, and made it possible for heavy bomber formations to undertake daylight raids under escort by North American P-51 Mustangs.
  The P-38 could also carry two 300-to-330-gallon drop tanks for its longest sorties. This teardrop-shaped tank design was 13 feet (4.0 m) long and 3 feet (0.91 m) in diameter at its widest point.
caption: A P-51 Mustang with 75-gallon metal drop tanks
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