 However shortly after the torpedo entered service it became apparent that newer Soviet submarines were both faster and deeper diving, and could potentially both outrun and out-dive the Mk.44 which was designed to attack targets with a maximum speed of only 17 knots.To address this an operational requirement was issued in 1960 resulting in the acceptance into service of the Mk.46 torpedo in 1963, when it began to replace the Mk.44 in U.S. service.A number of upgrade packages have been offered for the torpedo, a 1986 Honeywell kit replaced the magnetostrictive transducers with ceramic transducers in a planar array, and the replacement of the analogue guidance electronics with a digital system.