The Siebelfähre 40 (Siebel ferry 40), or just the SF40 for short, was a series of 200 shallow-draft catamaran landing craft developed by the Wehrmacht in 1941. Originally intended to be used for the planned invasion of the United Kingdom, it was later repurposed into a variety of roles: troop transport, ad hoc gunboat, floating flak battery, towed convoy escort, or even as a minelayer. Due to its simple design, the SF40 could be easily converted back and forth to fit various needs. The in-game “SF40 Heavy” is based on the specific SF40 outfitted with four 88 mm flak cannons deployed in Lahdenpohja on the Finnish-Soviet border.

Introduced in Update 1.79 "Project X" in the fleet closed beta test as the SF40 Schwere, the SF40 Heavy is the first of the slow but hard-hitting barges of the German coastal tree. It lives up to its “Heavy” designation thanks to a heavy armament of four 88 mm flak cannons, up to three of which can be targeted at a surface target at a time. This allows the SF40 Heavy to dismantle any lesser coastal vessel with a few well-placed hits, even at long ranges. However, the SF40 Heavy is quite slow and sluggish and therefore vulnerable at close range. Thus, it is advised to stay out of firefights and pick off the enemy one by one with your cannons.