32
	CHAPTER IV
	DIVING
	(i)  Diving Depths (B2).
	Tested Depth Boats are normally tested during working up under a pressure equivalent to a depth of 90 m. (295 ft.) in the pressure dock at Kiel.   Record Depth There is good evidence that one U-Boat in the summer of 1943 involuntarily dived to 340 m. (1,115 ft.) without breaking up.   Greatest Safe Depth Most Commanding Officers dive to 200 m. (656 ft.), the deepest safe depth to which they may go when being attacked.   Type VII/C.42 (See Chapter I.) This U-boat, not yet being used offensively (beginning 1944) dives to a maximum depth of 400 m. (1,300 ft.).   Type XB Minelayers Can only dive to 100 m. (328 ft.) with mines in the shafts.
	(ii)  Crash Diving Times (B2)
	500-tonners Periscope depth (13 metres 42.6 ft.) in about 30 seconds with original bridge and superstructure.   740-tonners Periscope depth in about 40 seconds.   1,200-tonners Periscope depth in about 45 seconds.   1,600-tonners Periscope depth in about 60 seconds.
	Crash diving times are materially increased by the addition of extra bandstands for additional A/A armament.
	(iii)  Diving Angles.
	During a normal crash dive, the angle tower increases from roughly 2 at the commencement to 10° as the bridge screen dips.  Thereafter the angle down is normally from 12-15°, though angles up to 45 have been reported, after complete submersion.
	Once submerged a U-boat can alter depth at the rate of 1-1/2 ft. per second.
	In the case of a snap encounter with a diving U-boat at close range, the after end presents a better target for the ram and (probably) the fore-end is at a more suitable depth for depth charges.
	(iv)  References.
	A table was published in C.B. 4050, June 1942, showing the average dives, turns and buoyancies of H.M.S. Graph (ex U. 570), a typical 500-ton U-boat.