On the northern banks of the Straits of Dardanelles, Eceabat, pop. around 5,000, is the nearest main town to WWI battlefields and memorials of Gallipoli Peninsula and serves as the hub to visit there. It also offers some accommodation options for those prefering a quieter and nearer alternative than Çanakkale.
In the absence of a bridge spanning the Straits of Dardanelles, the town is connected to Çanakkale by quite frequent (and 24-hr) ferries, accepting both passengers and cars/vehicles.
Since all buses operating between Istanbul and Çanakkale cross the Straits via Eceabat, it's possible to get on one in Istanbul and get off at Eceabat, most likely at the waterfront where they queue for the ferry.