Mines were the most potent part of many First World War submarines' arsenals because they preserved the boat's concealment. A close attack carried far more danger: once an escort found a submarine, ramming, gunfire, and depth charges could quickly become lethal. On her passage toward the Austro-Hungarian base network at Pola and Cattaro, U-73 laid fields off Lisbon, Malta, and Valletta's Grand Harbour approaches. Those mines accounted for the battleship HMS Russell, the sloop HMS Nasturtium, a trawler, and a yacht before Britannic encountered another field. This delayed threat helps explain why navies ordered minesweeping capability for later escort fleets. A submarine could make a waterway dangerous while already operating far away.
Notable Point · 2:07-6:47
U-73 shows why mines were a submarine's low-risk weapon
U-73's passage to the Adriatic demonstrates how a minelaying submarine could damage several ships after leaving an area and avoid the exposure required for a torpedo attack.