The British discovered that the depth charge damage to the U-boat was not critical—there were leaks in some of the ballast tanks and a small leak in a fuel tank. Around one third of the battery cells were cracked and the bow had been buckled. Water had leaked in through a valve that had been unseated by the explosions and through glass gauges that had broken; other damage was minor and no evidence of chlorine gas found. In his report, Colvin stated his opinion that there was no evidence of any damage control being carried out and that an experienced submarine crew would have been easily able to improvise repairs, stay submerged and likely evade the air-attack. After their surrender, the German crew had attempted to destroy instruments and fittings, but, with the exception of the wrecked radio and the damaged torpedo firing computer, the attempt appeared half-hearted and the damage was not significant. Also, useful papers had missed destruction. Copies of encrypted signals and their corresponding, plain-language, German texts were found—material of use to the British Enigma code breaking effort. A significant discovery was the U-boat commander's handbook, which provided context and background information for decrypted messages. The British, unfamiliar with German naval procedures, abbreviations and jargon, had often found German naval traffic hard to understand even when decrypted.