Mortars were weapons that fired explosive projectiles.
The Fourth Doctor killed a Rutan scout with a makeshift mortar at Fang Rock. (TV: Horror of Fang Rock)
The CyberKing had a mortar launcher on its right arm. (TV: The Next Doctor)
When Auderly House was attacked by the Daleks, the UNIT forces at the house used mortars to defend it. (TV: Day of the Daleks)
When the Third Doctor went to capture a brontosaurus, the Brigadier had his two of his soldiers set up a mortar in case he was attacked. They used the mortar when the Doctor was attacked by a tyrannosaurus rex, but it had no effect on the dinosaur. (TV: Invasion of the Dinosaurs)
A Roboform dressed as Santa used a mortar disguised as a tuba. (TV: The Christmas Invasion)