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. The overall effect of these changes was to triple the searched volume of the torpedo by increasing detection range by 75% and reducing the minimum shallow water search depth by 47%. With this modification the torpedo is known in South Korea as the KT44. A South African package offered an extensive upgrade, replacing the warhead with a 45 kilogram shaped charge device capable of penetrating 40 millimeters of steel behind a 1.5 meter water filled double hull. The package also included a comprehensive digital electronics upgrade tripling the target acquisition range to 1,000 meters in ideal conditions, and containing a number of counter-counter measures along with a variety of attack modes. The torpedo is, however, coming to the end of its usable life as the batteries have expired in many of the torpedoes. The New Zealand navy retired its Mark 44s in 1993 because it decided against renewing the batteries. Description The Mark 44 is a modular design, consisting of four main sections. The blunt nose contains the active sonar seeker with the 75-pound (34 kg) high-explosive warhead immediately behind it. The second section contains the guidance and gyroscopes. The third contains the 24 kilowatt seawater battery which uses silver chloride and magnesium electrodes with seawater acting as the electrolyte. Finally is the propulsion section which houses the electric motor, four rectangular control fins and two contra-rotating propellers. The vacuum tube-based guidance system is more sophisticated than earlier torpedoes, using pre-launch settings enabling an initial search depth of as well as a search floor at as well as a maximum dive/climb angle of 4.5, 6 or 7 degrees. On impacting the water the torpedo either runs out for or performs a dive at a 30-degree angle to the search depth. After completing this it may perform a flat turn and begins a helical search pattern proceeding up or down until it hits either the minimum depth of or the search floor. When it hits either top or bottom, it performs a flat turn and begins to execute the search in reverse. It continues executing this search until it either finds a target or exhausts its six-minute endurance. The guidance