A blast from my past - steam tanks inspired by the great Tremorden Rederring website. A heavy mobile casemate with three firing ports for her forward 12-pounder. She tows a Armstrong 40-pounder.
HMLS Oliphaunt wheezes forward, spear torpedo at the ready, a screen of sailors acting as skirmishers. Her semaphore ready to telegraph her next command.
SMDPW (His Majesty's Armoured Steam Wagon) Elfride; a light "raider" vehicle armed with little more than a single Gatling. Speedy at 12 kph.
UPDATE: Excellent TSaTF-based rules for steam inventions of all kinds - recommended.