HMS E3 (Lt Cdr G F Cholmley) was the first British submarine to be lost in war. She sailed with E8 to patrol off Borkum. On 18 October 1914, the U-boat U27 (Lt Cdr Bernhard Wegener) sighted what she thought was a buoy. On closer inspection, it was identified as a submarine conning tower, namely E3.

After stalking her for 2 hours, Wegener fired a torpedo at a range of 300 yards. E3 was hit, broke in half and sank at once. Four men were seen in the water but, worried that there may be other British boats in the area, Wegener did not pick them up. This was the first successful attack by one submarine on another. E3 was reported lost by Admiralty on 21 October 1914.