The Ordnance SBML two-inch mortar, or more commonly, just "two-inch mortar", was a British mortar issued to the British Army and the Commonwealth armies, that saw use during the Second World War and later.

It was more portable than larger mortars, and had greater range and firepower than rifle grenades. Its main purpose was to produce smoke for cover and through high trajectory and HE shell, engage targets "immune to small arms fire".

The two-inch mortar was one of a number of small mortars brought into service by European nations between the two World Wars.

Due to its small size, and for simplicity, the mortar had no forward strut or bipod like larger designs needed. The barrel was held at the correct angle by one soldier while the other loaded and fired the round. The original design had a large base plate and sights for aiming which used spirit levels. As the design matured, the baseplate became smaller and the sights were omitted; aiming was by eye and relied on the firer's judgment and experience. With such a short barrel, the typical firing method where the bomb was dropped down the tube and a pin in the base of the barrel struck the detonator in the tail of the bomb would not work, so firing was by a small trigger mechanism at the breech.

The bombs were cylindrical with a (perforated) four finned tail. For the HE projectile an impact fuze was fitted in the nose of the bomb.

Postwar, the two-inch mortar was kept in service to fire smoke and illuminating rounds. It was replaced by the Royal Ordnance 51 mm infantry mortar in the late 1980s.

Ammunition was packed one 51 mm-bomb per tube, three conjoined tubes per pack (three bombs), two packs (six bombs) to a fibre container, and three fibre containers to a steel box (18 bombs total).

India's Ordnance Factory Board's 51mm E1 mortar is an enhanced version of the two-inch British mortar of World War II; it is still in production and service in India.