These bombs are impact fired signal-generating, practice bombs used for training aircrews. The Mk 3 and Mk 4 bombs are unpainted with markings cast into the bomb body. The Mk 5 Mod 0 threw 3, Mk 23 Mod 0 & 1, and Mk 43 Mods 0 & 1 bombs are unpainted with markings cast or stamped into the bomb body. The Mk 3, Mk 4, Mk 5, and Mk 43 practice bombs are externally identical to the Mk 23 bomb.