By the end of May 1944, problems with releasing Highball had been resolved as had problems with aiming. Aiming Highball required a different method from Upkeep; the problem was solved by Wallis's design of a ring aperture sight fixed to a flying helmet.[36] Highball was now a sphere with flattened poles and the explosive charge was Torpex, enclosed in a cylinder, as in Upkeep; detonation was by a single hydrostatic pistol, set to fire at a depth of 27 feet (8 m), and its weight was 1,280 pounds (581 kg), of which 600 pounds (272 kg) was Torpex.[citation needed]
Highball was never used operationally: on 12 November 1944, in Operation Catechism, Lancasters with Tallboy bombs sank its primary target, Tirpitz. Other potential targets had been considered during Highball's development and later. These included the ships of the Italian navy, canals, dry docks, submarine pens, and railway tunnels (for which testing took place in 1943). But Italy surrendered in September 1943, and the other target ideas were dismissed as impracticable.[37]
In January 1945, at the Vickers experimental facility at Foxwarren, near Cobham, Surrey, a Douglas A-26 Invader of the USAAF was adapted to carry two Highballs almost completely enclosed in the bomb bay, using parts from a Mosquito conversion. After brief flight testing in the UK, the kit was sent to Wright Field, Ohio, and installed in an A-26C Invader. Twenty-five inert Highballs, renamed "Speedee" bombs, were also sent for use in the USAAF trials. Drop tests were carried out over Choctawhatchee Bay near Eglin Field, Florida, but the programme was abandoned, after the bomb bounced back at A-26C-25-DT Invader 43-22644 on Water Range 60, causing loss of the rear fuselage and a fatal crash on 28 April 1945.[38]
