British E-class submarines had fuel capacities of 50 long tons (51 t) of diesel and ranges of 3,255 miles (5,238 km; 2,829 nmi) when travelling at 10 knots (19 km/h; 12 mph).

The two submarines had orders to sail to the Baltic Sea to interdict German shipping, particularly vessels carrying iron ore shipments from Sweden.

[4] At around 01:00 on 18 August 1915, the submarine ran aground in shallow water near Saltholm island in the Øresund between Malmö and Copenhagen, because of a defective gyrocompass.

At 05:00 the Royal Danish Navy torpedo boat Narhvalen appeared on the scene and hailed the E13's commander, Lt Cdr Geoffrey Layton, informing him that he had 24 hours to refloat his vessel and leave before he and his crew would be interned for violating Denmark's neutrality.

[5] The E13's crew sought to lighten the submarine by pumping out tanks and discharging fuel, but she had grounded in only 10 feet (3.0 m) of water and would not move.

[6] Layton realised that he would not be able to refloat the E13 before the deadline passed and sent his first lieutenant ashore to arrange a tow or, if this was impracticable, to negotiate terms for internment.

[5][6] Meanwhile, the commander of the G132, Oberleutnant zur See Paul Graf von Montgelas, had informed Rear Admiral Robert Mischke by radio about the E13's grounding.

[9] Notwithstanding Denmark's neutrality, the dead British sailors were given full honours when their bodies were brought ashore, as a contemporary report described: There was a touching funeral scene to-night in the Sound.

Politiken reported that the Danish government had protested to Germany, pointing out that the E13 had not been destroyed in any kind of pursuit but while she was lying damaged on neutral territory.

[6] The London Times fulminated in a leading article that "the unjustifiable slaughter of the men of the E13 is one more notch in the long score we have to settle with the homicidal brood of Prussia.