IN 1940 THE LUFTWAFFE TRIED TO ELIMINATE THE ROYAL AIR FORCE during what would later be called the ‘Battle of Britain’.
They failed but according to some analysts came close, with a change in strategy targeting cities instead of airfields giving the RAF a chance to regroup.
Four years later a similar situation existed but this time Allied forces were sweeping through Europe, and their German counterparts were preparing to defend their homeland while British and American aircraft pounded German cities literally night and day.
Although Allied bombers were able to strike deep into Germany they could only have limited protection from their fighter escort before they had to return and leave the bombers at the mercy of the Luftwaffe.
And once again the defending fighters could conserve fuel – by this time in short supply – by taking off at the last moment to intercept the attackers.
Like the RAF in 1940, sometimes the German fighters could attack the bomber force, land, re-arm and refuel before once more engaging the homeward-bound Allied aircraft.
As the tides of war started to turn in favour of the Allies, their bombers reached further into Reich territory.
Although they were armed for self-protection the aircraft were vulnerable to enemy fighters on sorties that could last for nine or more hours.
They needed additional protection.
They needed fighters that could fend off the Luftwaffe – not just at close quarters to the bombers but ideally before they could position for an attack.
A fighter aircraft has to be fast, maneuverable, well-armed and ideally small enough to be difficult to see.
And above all light.
All of which imposes limits on its design with interdependent factors – an increase in (say) armament could increase weight and possibly aerodynamic drag and affect speed and range.
And range – how far an aircraft could fly was critical at this stage.
IWM LONDON’S example of a paper drop tank showing the differences in construction for the forward, centre and rear sections. Note the damaged left (port) rear section.
Image Copyright: © R Maddox 2019.
Jettison-able external fuel tanks (or ‘drop tanks’) were a relatively quick solution to increase their range.
These fuel tanks were able to be detached in flight, enabling the fighter to fly with the bombers and engaged the enemy, having dropped the external tanks.
After engagement the fighters would return on the fuel held in their internal storage tanks.
In June 1943 an American Republic P-47 Thunderbolt fighter could venture 230 miles from its base in England.
By August of that year the same aircraft fitted with external drop tanks could fly 375 miles – an increase of more than 60%.
By March 1944 a North American P-51 Mustang had a range of up to 600 miles. (1)
With metal in general – and aluminium in particular – at a premium and a valuable commodity that was salvaged by both sides from crashed aircraft that came down on their territories, an ingenious alternative was found by the RAF.
Paper. Laminated kraft paper.
This common product – used for cardboard packaging and things like brown envelopes – was very strong because of how it is produced. (2)
These tanks had a capacity of 108 US gallons (90 Imperial gallons) and although manufactured by British factories were used mainly by the ‘Little Friends’ – the fighter escorts of the 8th United States Army Air Force that accompanied the American bombers on daylight raids over Occupied Europe.
The tanks were cigar-shaped cylinders made in three sections – nose, tail and centre – all constructed with kraft paper reinforced resorcinol-formaldehyde glue, a waterproof adhesive that is resistant to ultraviolet rays. The paper itself has high tolerance to extremes of heat and cold – enabling them to be used in various theatres.
The middle section was made up of strips of the paper wound around a wooden cylinder in much the same way as a traditional toilet roll core is constructed. This tube then had plywood baffles fitted internally to support the structure and stop the fuel from surging from one end of the tank to the other. If this had occurred the trim and manoeuvrability of the aircraft would have been badly affected.
The tapered nose and tail ends were made up of specially pre-cut pieces, hand finished to get the smooth finish and curve required. Once the basic tank was finished fittings were added to enable the tanks to be filled, connected to the aircraft and the fuel to flow to the engine.
Then the tank was tested to six pounds per square inch to ensure its integrity. Finally they were finished with cellulose dope and then aluminium paint.
However it was found that fuel left within tanks for a period would slowly react with the glue and dissolve the tank and so the fueling and fitting to the aircraft was left as late as possible before take-off.
As previously noted the tanks were dropped before combat and usually landed in German or German-occupied territory and being paper denied recyclable metal to the Germans. But this also had an unexpected bonus.
The Germans had to produce leaflets in the areas where the tanks landed telling alarmed civilians that the tanks were empty fuel containers and not unexploded bombs. (3)
(1) Engineers of Victory – the problem solvers who turned the tide in the Second World War. Paul Kennedy (Allen Lane, 2013).
(2) https://www.jampaper.com/blog/what-is-kraft-paper/ – retrieved 30 November 2019.
(3) http://warbirdsnews.com/warbird-articles/necessity-mother-invention-paper-drop-tanks-wwii.html – retrieved 30 November 2019.