E23 torpedoed the German dreadnought SMS Westfalen (18,900 tons), holing her off Terschelling on 19 August 1916.

British E-class submarines had a fuel capacity of 50 t (55 short tons) of diesel and ranges of 3,255 nmi (3,746 mi; 6,028 km) when travelling at 10 kn (12 mph; 19 km/h).

[2] E23 was capable of operating submerged for five hours when travelling at 5 kn (5.8 mph; 9.3 km/h).

E23 was armed with a 12-pounder 76 mm (3.0 in) QF gun, mounted forward of the conning tower.

[3] E-class submarines had wireless systems with 1 kW (1.3 hp) power ratings; in some submarines, these were later upgraded to 3 kW (4.0 hp) systems by removing a midship torpedo tube.