Testing
of Upkeep prototypes with inert filling was carried
out at Chesil Beach, Dorset, flying from RAF Warmwell
in December 1942, and at Reculver, Kent, flying from
RAF Manston in April and May 1943, at first using
a Vickers Wellington bomber. However, the dimensions
and weight of the full-size Upkeep were such that
it could only be carried by the Avro Lancaster, which
was the largest British bomber available at the time,
and nonetheless had to undergo considerable modification
in order to carry it. In testing, it was found that
Upkeep's spherical casing would shatter on impact
with water, but that the inner cylinder containing
the bomb would continue across the surface of the
water much as intended. As a result, Upkeep's spherical
casing was eliminated from the design. Development
and testing concluded on 13 May 1943 with the dropping
of a live, cylindrical Upkeep bomb 5 miles (8 km)
out to sea from Broadstairs, Kent, by which time Wallis
had specified that the bomb must be dropped at "precisely"
60 feet (18 m) above the water and 232 miles per hour
(373 km/h) groundspeed, with back-spin at 500 rpm:
the bomb "bounced seven times over some 800 yards,
sank and detonated" |