In the summer of 427 BC, the Spartans and their allies planned a concerted effort on land and sea to strain Athens' resources and relieve the siege at Mytilene. The annual invasion of Attica that year was the second largest of the Archidamian War, exceeded in duration and destructiveness only by that of 430. While this invasion was underway, 42 ships under the command of the navarch Alcidas were sent out to Mytilene; the plan was that the Athenians would be preoccupied with the invasion and unable to devote their full attention to Alcidas and his fleet.