Military uses of time travel are abhorrent, much like those of submarines. And like submarines they are being developed by every major power. What follows is largely theoretical, since to date (so far as is known) this technology has only been used in naval exercises.
The simplest use of time travel is for direct attacks; a time ship identifies an enemy craft at a distance, dives into the past while simultaneously closing with it, then returns and "surfaces" in the present for the attack. While the Temporal Displacer is working the warship is immune from attack, unless it has the misfortune to come under fire or hit a mine in the short time it must spend in the past to change its temporal direction. There are snags, of course; if things go badly wrong the warship might have to fight in the past as well as the present, without any possibility of affecting the enemy's ability to fight the final battle. Time spent in the past can't be recovered; if the manoeuvre takes five minutes, the attacker will "surface" five minutes after it vanished, and in that time the enemy may have changed course, sent a wireless message requesting help, or received reinforcements. For these reasons warships need to be big and fast, capable of closing with an enemy quickly and changing temporal "course" so far in the past that there is little possibility of hitting a mine or engaging the enemy without adding any unnecessary delay. Even then it's difficult to guess which strategy would be most effective. For example, the proposed battleship Dreadnought at 18,110 tons (multiplier 4.47), maximum speed 21 knots, might attack a target 20 nautical miles away. She could dive back into the past for 30 minutes, travelling 10.5 nautical miles and going back 14.17 years, change temporal course, and return to the present. It's unlikely that the enemy would happen to (a) be the enemy and (b) have ships or mines at exactly the right place that far in the past. The Dreadnought closes the remainder of the gap and "surfaces"... but of course the enemy has had an hour to prepare for the fight, and may have changed course as soon as the Dreadnought vanished! It might be a better idea to use short jumps instead. In the case above the Dreadnought could take some five minute jumps, closing by 3.5 miles between one sighting and the next in each ten minute jump, firing at the enemy then vanishing into the past before fire could be returned, but would only travel back 24 days in five minutes and might still be in danger when it changed temporal "course" in the past. Cases can be made for and against every possible combination of moves and it will take bitter experience, and consequent loss of life, to determine which are correct.
A less problematic use is to travel without any possibility of interception, returning to the present at an agreed place and time to rendezvous with other vessels before going into action. It's necessary to ensure that all spend the same amount of time travelling, but that's simply a matter of planning appropriate routes. For example, if the Dreadnought had to sail from Portsmouth to attack Kiel (a trip of about 1100 nautical miles) she might drop back a hundred thousand years or so in ten hours, steaming 210 miles with the temporal displacer active, steam 700 miles or so normally, then start to return to the present after passing Goteburg, finally "surfacing" well inside Kiel's outer defences. It's notable that since this technique was first suggested (in an article by Mr. H.G. Wells on the future of naval warfare which appeared in The Strand Magazine, April 1894) most of the global Powers have strengthened harbour defences, laid more mines, etc.
One technique that is theoretically possible, but hopefully will never be tried, is to carry out probing attacks against an enemy in the very near past (a figure of five or ten minutes has been suggested), observe how the enemy responds, then use the information obtained to carry out a "real" attack against an enemy who does not know that you have repeatedly attacked his shores or fleet. Of course this assumes that you are prepared to risk losses, but combined with the other techniques outlined above they would probably be light.
Some disturbing possiblities exist for espionage. Briefly, it would be possible to land spies a few hours in the past and send them to obtain any desired information. If they are caught the ship returns to the present, leaving the spies to vanish along with the world in which the enemy are aware that espionage has taken place! It might even be possible to use spies from the earlier period, so that nobody from the present takes any risk. Even in the murky world of espionage there are probably agents prepared to take this chance in the knowledge that a later version of themselves will continue to exist.
Okay - any additional tricks?