Megaton

 was a unit of measurement for the power of explosions in use by humans, the Doctor, K9 and Davros. (TV: Terror of the Autons, Underworld, Destiny of the Daleks)

planted a fifteen-megaton bomb on Jo Grant in order to destroy the Third Doctor and UNIT; the Doctor threw it out the window and boiled out the contents in time. (TV: Terror of the Autons)

The Oracle sent a pair of two-thousand-megaton bombs were intended for the to eradicate R1C, but ended up destroying itself. K9 identified that it was impossible to defuse it. (TV: Underworld)