Why arm landing craft with 17-pounders?

Why were 17-pounder guns fitted to landing craft?

They were Britain's strongest readily available anti-tank weapon, with 25-pounders providing an even heavier alternative for shore bombardment.

British planners expected armour to counterattack landing beaches and designed for a more active defence than Allied troops ultimately encountered on D-Day. The assault also had to defeat pillboxes and other hardpoints. Smoke, flames, and friendly troops could keep battleships or cruisers farther offshore from engaging close targets safely. Mounting 17-pounders or 25-pounders on armoured landing craft put responsive direct fire into the assault wave. Naval and Army crews also held a training competition over how quickly they could fire 25-pounders, with the naval team narrowly winning. Gunnery depended on drill as well as calibre and mounting.