Intercept the Reinforcements

Here's how to complete the quest:

-Go over to the Dragonhawk flight master (the same one you start the bombing run over The Dead Scar).

-Select the bombing run option.

-Make sure you have the bomb in your bag and ready to fire.

-You fly by each ship (as seen in the screenshot). Throw one bomb onto each ship. One bomb will give you credit for the ship.

-Once you land, start killing the Reservists on the ship. If one ship is entirely full, try one of the other two.

-Once done, go back to the original ship you landed on. There will be a Dragonhawk there. Talk to it, and select "Take me back".

-Turn it in and enjoy the rewards.

Upon recovering the Sun's Reach Harbor (completion of phase 3), this quest is replaced by Keeping the Enemy at Bay, which has the same objective but is a permanent daily quest that can be completed for reputation and reward, and will always be available once it is unlocked.

For more information regarding the Shattered Sun Offensive daily quests and the "phases" of reclamation, check out this guide on the Wowhead forums! :)

NOTE : You do NOT have to be flying on the dragonhawk to burn the ships with the oil. You just have to use the item nearby to where you're in range, even on foot or swimming to the ships.