Where the objective of the expedition is not the local naval base, the choice of a position for the covering squadron will turn mainly on the amount of support which the army is likely to require. If it cannot act by surprise, and serious military resistance is consequently to be expected, or where the coast defences are too strong for the transport squadron to overpower, then the scale will incline to a position close to the army, though the extent to which, under modern conditions, ships at sea can usefully perform the delicate operation of supporting an infantry attack with gun fire, except by enfilading the enemy's position, remains to be proved. A similar choice will be indicated where strong support of men and boats is required, as when a sufficiency of flat-boats and steam towage cannot be provided by the transports and their attendant squadron; or again where the locality is such that amphibious operations beyond the actual landing are likely to be called for, and the assistance of a large number of boats and seamen acting with the army is necessary to give it the amphibious tactical mobility which it would otherwise lack. Such cases occurred at Quebec in 1759, where Saunders took his covering battle-squadron right up the St. Lawrence, although its covering functions could have been discharged even better by a position several hundreds of miles away from the objective; and again in 1800 at Alexandria, where Lord Keith ran the extremest hazard to his covering functions in order to undertake the supply of General Abercromby's army by inland waters and give him the mobility he required. If, on the other hand, the transport squadron is able to furnish all the support necessary, the covering squadron will take station as close as possible to the enemy's naval base, and there it will operate according to the ordinary laws of blockade. If nothing is desired but to prevent interference, its guard will take the form of a close blockade. But if there be a subsidiary purpose of using the expedition as a means of forcing the enemy to sea, the open form will be employed; as, for instance, in Anson's case above cited, when he covered the St. Malo expedition not by closely blockading Brest, but by taking a position to the eastward at the Isle de Batz.