[Gwaihir the Windlord]

Certainly an interesting battle, Rumil.

It is indeed the only naval battle encountered anywhere in Tolkien's mythos, I believe, the reason for this of course being that cannon were not yet in existence -- the weapons that would transfer warships from, primarily, troop-carriers into vessels more able to fight each other directly. Thus, as in pre-gunpowder times in our own world, battles in ME were usually fought between men personally and not between ships.

Sea battles did exist before cannon, though rarer and in a very different form. Ships would draw together and the men inside them fight, basically, which is what I'm guessing would have taken place here. It is imaginable that other tactics could also be attempted other than the usual (I believe) that one of attempting boarding; extremely heavy ships against lighter ones could try to ram, or use ballistae in place of artillery, perhaps! I've never heard of it, but it may have been done.

(I too would appreciate any information on this that anyone could add -- my knowledge of the era of cannon-bearing ships is good, but before that, I'm not totally sure about it.)

The battle itself can therefore probably be guessed. They draw in by night, come up beside the Corsair ships in harbour, and attack them. The pre-powder way to destroy ships is presumably to burn them, so with the aid of oil or tar or something they would have been able to set light to many. Large Corsair war-galleons would have withstood the running-over or ramming tactic, but maybe a few of the smaller ones were sunk in this manner.

A quick firing of the local port area, and then a speedy withdrawal back to Pelargir leaving the place in turmoil, would probably have followed.

But Thorongil's fleet -- what ships, indeed? We don't know, although Gondor certainly had a large navy in the past (and the Numenorean kingdom was of course a maritime nation in origin). It may well be that Gondor had a navy in the late Third Age; but remembering the lesser function of navies in pre-cannon times, the apparent inaction of any Gondorian navy in the War of the Ring may be due to the fact that it wasn't really possible. Could these ships have actually done anything? Blockade Anduin, perhaps, which would slow down the Corsairs, but not Umbar. The huge-scale blockade of French ports, staged by the Royal Navy in the Napoleonic wars, was extremely effective but under a different circumstance, as again, these ships were equipped with guns and would have actually fired on French ships if they ever attempted to leave. A blockade on Umbar would have been an ill-fated venture, as Umbarin ships could mass, break out and mob the Gondorian ships, boarding and battering down the defenders of the restraining fleet, or simply sailing past them. Gondor could not have kept up such a blockade. Umbar had overwhelming ship resources.

They could perhaps have stationed themselves off the coast, and then attacked individual Corsair ships as they sailed to Pelargir, but either way it is not really a matter of much surprise that they were inactive (if a navy existed). Attention was on the main land army of Mordor, the defence of Minas Tirith, and remembering the chaos that was happening at this time -- most efforts were bent on the Mordor frontier -- the matter of the navy, which could have been grounded by Denethor as you say (although I feel this to be unlikely. Denethor was jealous of Aragorn, but until the Palantir turned him insane he was not this kind of fool) or neglected in the face of other concerns.

I should say that some ships did exist in the Steward's service, stationed at Pelargir, in the time of Ecthelion II. Gondor was, at this time, still in good order and was not immediately on the spot it had been burning under, for years, by 3020; the navy would perhaps not have yet been neglected. Of course, we don't know much at all for sure. Not much information on this one, unlike the Fords of Isen.