Brazil ordered the ships from Vickers for patrol work on the Amazon, where shallow water, tributaries, and long river passages demanded a broad, shallow-draft vessel. The hull measured about 81 metres long and nearly 15 metres wide, with a standard displacement of 1,280 tons and a full-load displacement of 1,540 tons. A draft of only 1.7 metres suited river and coastal work, although a practical speed of about 9.5 knots left the design far from ocean-going. A twin 6-inch turret, two 4.7-inch howitzers, light guns, an anti-aircraft gun, and machine guns packed substantial firepower into the compact hull. Those specifications made the river gunboats well suited to British operations close to hostile shores.
Chapter · 7:43-10:32
A Brazilian river gunboat becomes a coastal monitor
The Humber class began as Brazilian Javary-class gunboats whose shallow draft and compact armament suited difficult river and coastal waters.