a missile submarine is also not relevant since it can stay submerged for very long periods of time, and is not expected to ever cruise on the surface when in range of enemy units of any type. A WWII era submarine (technically a submersible since it is only capable of diving for limited periods of time) is by design forced to spend much of its time on the surface, and therefore needs to be able to "escape" by diving when an enemy is spotted. A WWII-era submarine is also very small, with a periscope depth of only a dozen or so feet, compared to a modern ballistic-missile submarine, which has a periscope depth of up to 100 or more feet deep. In extreme emergencies, submarines have had to crash dive so quickly that lookouts were left on-deck. Such was the only survivor of U-68 when the four lookouts were left top-side as she crash dived among exploding aerial bombs. Commander Howard Gilmore earned the Medal of Honor posthumously during World War II by ordering a crash dive ("Take her down!") while wounded and unable to leave the bridge of . See also Emergency main ballast tank blow Notes and references Notes References Submarine tactics