I know the safety lock is in a form of a tiny propeller that spins itself off a threaded shaft and falls away after the torpedo runs about 30 yards, thus arming the torpedo. I do not know why Ballard considered it dangerous just sitting in the tube. As to the "No hiss" I figure in writing his book he may have had first hand information from that time in the form of a diary, log, newspaper report etc. as his sources. My main concern for accuracy with the technology of that time is can a misfired torpedo be repaired at sea? And how was it done? My theory - Close outer torpedo tube doors, expell the water from the tube (could a WWI boat do this?), haul the tin fish out with block and tackle and do maintenance? The WWI U-boats were not as technologically advance as the WWII boats, that I know. Thanks again for your help.