The Spanish, English and Dutch fleets are shown assembled in the waters off the coast of Kent, between Deal Castle, a Tudor fortress constructed exactly one hundred years before, and Sandwich, which was the site of one of Britain's major ports, as well as the namesake of delicacy invented there. Although the title, in a square cartouche in the lower left-hand corner, states that the image shows the "assembly before the battle...in 1640", it actually depicts the prelude to the Battle of the Downs, which took place on 21 October 1639.

The battle formed part of the Eighty Years' War between Spanish and Dutch forces. Spain was making an attempt to re-assert naval control over the English Channel, challenging decades of Dutch dominance over the sea lanes. The Spanish leader Admiral Antonio de Oquendo took refuge in The Downs, an anchorage between the ports of Dover and Deal. Here English neutrality offered some protection, allowing most of the reinforcements to avoid the Dutch blockade by using small, fast frigates. Eventually the Dutch entered the Downs and attacked the Spanish fleet, which was unable to manoeuvre in the cramped waters, and thus lost many chips. The Spanish defeat off the Kentish coast only helped reinforce Dutch supremacy over the waters.

Deal Castle is shown in the centre of the right hand sheet, with various figures in and around the distinctive rose-plan fortress. Numerous ships are visible on the sea in the background, identified in an alphabetical key in the lower right-hand corner. The key also shows the village of Deal on the left, again with the fleets assembled in the background. A small crowd of English men and women are gathered on the hillside looking out at the ships.