Warcraft II: Tides of Darkness/Runestone at Caer Darrow

Story
Since many of the necessary structures were already in place, Urok's unit's first task was the collection of resources for the invasion. Farms and slaves were created at a dizzying pace; tankers set out southward to install a platform and collect oil. Their warships stayed close to shore with a zeppelin overhead; their stronghold and towers were upgraded as soon as their supply of resources permitted. Construction continued with a foundry, refinery, and a goblin alchemist to produce more fliers for the invasion. A second shipyard was erected to double their juggernaugt production, and soon they had a powerful flotilla in the bay.

Six massive juggernauts sailed out with a zeppelin overhead to spot enemy submersibles, and they began the slow process of pounding the defenses on the central island. Keeping the ship together, they made constant strikes on single targets, then sailed back out of range to regroup. Enemy ballistas were drawn out to shore for their destruction. With most of the towers removed, they started on shipyards at both villages. Many of their juggernauts were sunk in the process, but more were constantly produced to replace them. Once the Alliance's naval power was decimated, the juggernauts moved in close to shore on the island and removed most of the land structures to make way for a landing.

While the island was being pounded, an ogre mound went up within the Horde's base and twelve ogres were loaded on transports to assault the island. Resistance was minimal and soon the runestone was theirs. This sent a clear signal to the remaining humans in the other village, who beat a hasty retreat. Urok believed their might was growing daily and that their morale was higher than it had ever been, even during the destruction of Azeroth.

Alternate strategy
Another more subtle way to take the island is to avoid the island entirely, at least initially. Bring your juggernauts and transports to the easternmost part of the screen, destroying the few ships in your way. Keep a zeppelin above to keep watch for submarines. Go south until you see their southeastern base, where their only goldmine is located. Blow up the units and buildings that your juggernauts can reach, then unload your transports to kill their peons and destroy their town center (keep or castle, whichever you want to call it). Their economy thus stunted, they will lose the ability to create new units, making the island in the center much easier to capture using the method advised above.