According to the Martian Technology Report: The Martians made surprisingly little use of any analogue to terrestrial artillery. For the most part they relied upon their Heat-Rays to quash any resistance to their conquest. The only occasion on which they used any sort of ballistic weapon was in the delivery of their dreadful canisters of Black Smoke. This powder was dispensed by means of canisters fired from reusable tubes, wielded by the Martian Fighting Machines."
The Magnetic Acceleration Cannon consisted of a hollow tube containing a great many rings of a similar material to the discs of the pseudomuscular structure, having virtually no electrical resistivity. It is believed that a powerful electrical current was exerted upon each ring in turn, strongly magnetising them and accelerating the canister of Black Smoke, which was ceramic bound with bands of a ferrous substance, towards its target. Each firing tube, once expended, was discarded (presumably to be reloaded at a later time), and another tube taken up. The loud report that characterised the firing of the Black Smoke is believed to be that of the canister accelerating past the speed of sound.
It is possible that the Magnetic Acceleration Cannons could fire a variety of shells, from the Black Smoke canisters deployed against the British military, to explosives or incendiaries. No such shells were discovered among the artifacts left by the Martians, so it must be presumed that they were sufficiently confident in the capabilities of their Black Smoke to silence opposition that they regarded other types of ammunition to be unnecessary.