King Rama V ordered at great expense the latest guns from W G Armstrong & Co in England. These were ten 6 inch Armstrong Guns which weighed five tons each. They were the first rear-loaded guns in the Thai Navy and they had an interesting characteristic. They were called the “disappearing” guns because they only came out of the pit to fire and then the recoil forced the gun back where it came from. This protected the guns from enemy fire. That was the theory. All of the aiming had to be done while the gun was in the pit. Each shell weighed 45 kilos. The gun was then hauled up be a hydraulic mechanism and the shot fired. The range was about 8 kilometres.
Seven of these guns were installed at the Phra Chulachomklao Fort. The remaining three were set up at Phi Sua Samut Fort which is an island in the middle of the river. About three months after their completion they saw action for the first and only time. On 13th July 1893, two French gunboats entered the estuary with the intention to blockade Bangkok. Shots were fired and a small boat that was acting as a pilot for the French ships was badly damaged and ran aground. Despite heroic action by the soldiers at the fort and the sailors aboard ships on the river, the two French gunboats managed to slip by. By the time it reached the inner fort it was too dark for anyone to continue the battle. The gunboats were then able to go all the way up the river to Bangkok.