Although the P.108A proved to be capable, and fired over 280 shells in testing, the Armistice and the never-ending change of priorities halted its development. The use of such large aircraft in a dangerous anti-ship role was however questionable (though the USA very successfully used B-17s to skip-bomb Japanese boats at close range & sea level) with at sea level speeds 360 km/h (220 mph) was the best safely achievable, the cost was even greater than standard bombers, and the improved naval anti-aircraft defences (Bofors 40 mm guns, P-F shells, and fire-control radar) led Germany to develop glide bombs like the Henschel Hs 293 and Fritz X.