A successful torpedo drop required that the approach run to the target needed to be straight and at a speed and height where the torpedo would enter the water smoothly: too high or too low and the torpedo could "porpoise" (skip through the water), dive or even break up. Height over the water had to be judged without the benefit of a radio altimeter and misjudgement was easy, especially in calm conditions. For the Beauforts using the 18-inch (450-mm) Mk XII aerial torpedo, the average drop-height was and the average range of release was . During the run-in, the aircraft was vulnerable to defensive anti-aircraft fire and it took courage to fly through it with no chance of evasive manoeuvres. The Beaufort's optimum torpedo dropping speed was a great deal higher than that of the Vildebeests it replaced, and it took practice to judge the range and speed of the target ship. A ship the size and speed of "Scharnhorst" would look huge, filling the windscreen at well over and it was easy to underestimate the range. In action, torpedoes were often released too far away from the target, although there was one recorded instance of a torpedo being released too close. For safety reasons, torpedo warheads had a set distance (usually about from the release point before they were armed. It also took some distance for the torpedo to settle to its running depth. Once the torpedo had been dropped, if there was room, a sharp turn away from the enemy was possible: more often than not the aircraft had to fly around or over the ship, usually at full-throttle and below mast height. A sharp pull-up could be fatal as it exposed a large area of the aircraft to anti-aircraft guns.