UB-4 was a little more than 28 metres (92 ft) in length and displaced between 127 and 142 tonnes (125 and 140 long tons), depending on whether surfaced or submerged.

[7][Note 3] UB-4 was part of the initial allotment of eight submarines—numbered UB-1 to UB-8—ordered on 15 October from Germaniawerft of Kiel, just shy of two months after planning for the class began.

The process of shipping a UB I boat involved breaking the submarine down into what was essentially a knock down kit.

[11][Note 4] UB-4 soon joined the other UB I boats then comprising the Flanders Flotilla (German: U-boote des Marinekorps U-Flotille Flandern), which had been organized on 29 March.

During this campaign, enemy vessels in the German-defined war zone (German: Kriegsgebiet), which encompassed all waters around the United Kingdom (including the English Channel), were to be sunk.

[19][20] The 1,954 GRT steamer had sailed from Dunston and was headed to Bordeaux when sunk 1.5 nautical miles (2.8 km; 1.7 mi) from the Shipwash Lightship off Harwich.

[20] On 14 August, the 59 GRT British fishing smack Bona Fide was stopped by a U-boat, boarded, and sunk with explosives 35 nautical miles (65 km; 40 mi) east-northeast of Lowestoft.

[22] Regardless of the identity of Bona Fide's attacker, UB-4 did approach a group of smacks in the vicinity the next day, but unbeknownst to UB-4's commander, Gross, one of the fishing vessels was actually a British decoy ship.

A burst of three rounds from the 3-pounder scored hits on the conning tower, the second destroying part of the bridge and sending Gross into the water.

A member of Inverlyon's crew attempted the rescue of one crewman from UB-4, but was unable to reach him before he went under, meeting the same fate as the other thirteen crewmen.

The Q-ship's crew, not having a wireless set on board, sent word of the encounter with another smack, and followed up by releasing messenger pigeons the following morning, requesting instructions on what to do with UB-4.

The thought of salvaging the snagged U-boat was rejected, so the nets were cut, freeing UB-4 to sink to the bottom.

[4] Jehan was awarded the Distinguished Service Cross for the sinking of UB-4, and the crewmen of Inverlyon split the submarine bounty paid by the Admiralty.