This counterguard is located in front of Orange Bastion and faces the present Queensway. The purpose of a counterguard was to serve as an outwork in a bastioned fortification, comprising a relatively low rampart, situated in front of the existing bastion behind it. The counterguard was so constructed to be wide enough to enable the positioning of artillery and this was the case with the Chatham Counterguard which could mount a total of ten guns. The Rock Model in the Gibraltar National Museum shows three embrasures on the left, five on the right flank and two the right flank. Its purpose was to act as an outer line of defence and as a cover against bombardment of the bastion behind, whose shape it mirrored. Drawings were prepared on 6th March 1790 showing the state of the proposed work on improving the Waterport Front and all the surrounding area. They showed a considerable development from earlier plans submitted by the Chief Engineer, Lt. Col. Robert Pringle, in January 1787. Montagu Bastion would be enlarged into a pentagonal bastion and this would also be the case with Orange Bastion which would project its right flank and shoulder well forward. Beyond these bastions, new counterguards (site of the present Montagu and Chatham Counterguards), were to be raised a foot and a half above high-water mark, so as to replace the earlier proposal for a covered way and places of arms. Beyond them, a reef of dry rubble walling would be erected in the sea to bar the approach of any amphibious assault. Work on the counterguard were completed by 1804 and its original name of Orange Counterguard was later changed to Chatham Counterguard after the Governor of Gibraltar, John Pitt, 2nd Earl of Chatham.