Depthcharge is an arcade game that was released by Gremlin Industries in 1977; it runs on a Zilog Z80 microprocessor (running at 1.93356 MHz), and is the first game from that company that is not a variant on Blockade. The player must use two directional buttons to move a boat left and right at the top of the screen, while using two additional buttons to drop depth charges to the left and right - and you can have a maximum of six depth charges on screen at a time. You will have ninety seconds to destroy as many submarines as possible; each submarine has a number (ranging from 10 to 90) on it, which indicates how many points it is worth if destroyed. Those submarines will also occasionally release mines that will float up towards your boat which must be avoided - and for good reason too, because every time one hits the boat, it will reduce the score for all subsequent submarines by half. Every submarine that you manage to destroy will be indicated at the bottom of the screen in what is referred to as the "graveyard"; at the end of a game a player will receive a 30-point bonus for every submarine in there. Scoring over 500 points at the end of the game will also result in 45 seconds of extended play - and Sega's Deep Scan, released two years later, also features similar gameplay to this title. However, it was only ever available in two dual-game cabinets, with Invinco or Head On 2.