G-5 speed depended on relentless corrosion control

The G-5 used a single-step hydroplaning hull and stern-cradle torpedoes, with later variants drawing formidable speed from aircraft-derived engines. Its duralumin combined aluminium and copper, making corrosion control in salt water an operational necessity. A captured Soviet officer's account says the boats might remain afloat for only a week in summer or two weeks in winter before being lifted for treatment. The source material does not establish whether the prisoner was a commander or another officer, and prisoners had reasons to claim higher rank for better treatment. Production variants changed displacement, weapons, engines, and reported speed, with some figures reaching the mid-fifties in knots. The forced lifting cycle may have kept the G-5s in better condition than the neglected SH-4s because crews could not postpone basic hull care. The boat's headline performance depended on a demanding maintenance burden.