It seems probable that at least one purpose of the chain was to hinder the progress of fire-ships which the enemy set in motion against our shipping.
In order to defend the government works nearer London, batteries mounting sixty pieces of ordnance were erected at Woolwich, whilst the defensive works at Gravesend and Dover were strengthened.
About the middle of the following September workmen were employed in clearing away the moorings of the chain at Gillingham Reach.
Chains at Portsmouth, Great Yarmouth, etc.—The chain of Chatham furnishes a curious example of coast defence, wholly ineffective against powerful shipping; but it was not a novelty. Portsmouth Harbour had been at an earlier period provided with a similar form of defence. Edward VI, on the occasion of a visit to Southsea Castle, determined to strengthen Portsmouth against invasion by the enemy. He therefore directed the building of two massive towers at the entrance to the harbour. To these an immense iron chain was fixed in such a way that it could be raised and tightened or lowered at pleasure when the approach of the enemy made this desirable. The fortifications of Portsmouth were strengthened during the reign of Elizabeth (see [p. 145]).
Great Yarmouth.—In addition to a boom and two timber jetties at the entrance to the haven, Yarmouth possessed a chain for the protection of its shipping.
Hull possessed a chain, and an actual picture of it is preserved in one of the Cotton MSS.
Cowes also was defended by a chain.
Fowey.—For the protection of this town Edward IV erected two towers to carry a chain which was suspended, doubtless under the level of the water, across the haven, or mouth of the River Fowey. Subsequently the people of Fowey incurred the royal disapproval when they attacked the French during a truce, and accordingly Edward IV had the chain removed and sent to Dartmouth. It does not seem quite clear whether this chain, when removed to Dartmouth, was used for the protection of shipping, but there certainly was a chain bridge at this place in which, conceivably, the old chain may have been utilized.
There is reason to think that chains for the protection of important centres of shipping were more common than might be supposed from the few definite particulars of them which have survived. As an effective defence against the approach of the war-ships of an enemy, however, it would perhaps be impossible to find a more feeble type of protection.
Booms.—As we have already observed in dealing with chains, the necessity must have been felt of supporting such very heavy barriers, even under water and by means of buoys. The boom, although introduced quite early, must have been an improvement upon the simple iron chain, because it contained, to some extent, its own means of support. This contrivance, a chain of linked up massive timbers reinforced with iron, and armed with iron spikes was employed, as early as the time of Queen Elizabeth at Great Yarmouth, and subsequently at many other ports. Like the chain it, of course, provided an obstruction to navigation, especially at the mouths of rivers and harbours; but its massive iron spikes, calculated to pierce and damage shipping, gave it a distinct advantage over the chain.