An inflatable boat is a lightweight boat constructed with its sides and bow made of flexible tubes containing pressurized gas. For smaller boats, the floor and hull are often flexible, while for boats longer than 3 metres (9.8 ft), the floor typically consists of three to five rigid plywood or aluminium sheets fixed between the tubes, but not joined rigidly together. Often the transom is rigid, providing a location and structure for mounting an outboard motor.
Some inflatable boats can be disassembled and packed into a small volume, so that they can be easily stored and transported. The boat, when inflated, is kept rigid cross-ways by a foldable removable thwart. This feature makes these boats suitable for liferafts for larger boats or aircraft, and for travel or recreational purposes.
There are ancient carved images of animal skins filled with air being used as one-man floats to cross rivers. These floats were inflated by mouth.
The discovery of the process to vulcanize rubber was made by Charles Goodyear in 1838, and was granted a US patent in 1844. Vulcanization stabilized the rubber, making it durable and flexible. In late 1843, Thomas Hancock filed for a UK patent, which was also granted in 1844, after the Goodyear Tire and Rubber Company patent had been granted. In 1852, while traveling in England, Charles Goodyear discovered that Thomas Hancock's company was producing vulcanized rubber and sued. Thomas Hancock had been shown a sample of Goodyear's rubber in 1842, but had not been told the process that made it—and Hancock said he had developed his process independently. The last of the suits were settled in 1855. Shortly thereafter, several people expanded on experimentation of rubber coated fabrics.
In 1839 the Duke of Wellington tested the first inflatable pontoons. In 1840, the English scientist Thomas Hancock designed inflatable craft using his new methods of rubber vulcanization and described his achievements in The Origin and Progress of India Rubber Manufacture in England published a few years later.
In 1844–1845, British naval officer Lieutenant Peter Halkett developed two types of inflatable boats intended for use by Arctic explorers. Both were made of rubber-impregnated "Mackintosh cloth." In the Halkett boat, the "boat cloak" served as a waterproof poncho or cloak until inflated, when it became a one-man boat. A special pocket held bellows for inflation, and a blade to turn a walking stick into a paddle. A special umbrella could double as a sail. Halkett later developed a two-man boat carried in a knapsack. When inflated, it could carry two men paddling on either side, and when deflated it served as a waterproof blanket for camping on wet ground. The Admiralty was sceptical about potential uses for Halkett's designs; on 8 May 1845, Lord Herbert, First Secretary to the Admiralty, wrote to Halkett that "My Lords are of an opinion that your invention is extremely clever and ingenious, and that it might be useful in Exploring and Surveying Expeditions, but they do not consider that it would be made applicable for general purposes in the Naval Service".
The Admiralty saw no use for Halkett's designs in general naval service, but explorers liked this larger design. John Franklin bought one for the ill-fated 1845 expedition, in which the entire expedition party of 129 men and two ships vanished.
In his explorations along the Oregon Trail, and the tributaries and forks of the Platte River in 1842 and 1843, John C. Frémont recorded what may have been the first use of an inflatable rubber boat for travel down rivers and rapids in the Rocky Mountains. In his account of the expedition he described his boat:
Among the useful things which formed a portion of our equipage, was an India-rubber boat, 18 feet long, made somewhat in the form of a bark canoe of the northern lakes. The sides were formed by two airtight cylinders, eighteen inches in diameter, connected with others forming the bow and stern. To lessen the danger of accidents to the boat, these were divided into four different compartments, and the interior was sufficiently large to contain five or six persons, and a considerable weight of baggage.
In 1848, General George Cullum, the US Army Corps of Engineers, introduced a rubber coated fabric inflatable bridge pontoon, which was used in the Mexican–American War and later on to a limited extent during the American Civil War.
In 1866, four men crossed the Atlantic Ocean from New York to Britain on a three-tube raft called Nonpareil.
From 1900 to 1910, the development of rubber manufacturing enabled attempts at producing circular rubber inflatable boats, similar to modern coracles. These were only usable as rafts, and could only be propelled by paddling. In addition, they tended to crack at seams and folds due to the imperfect manufacturing process of the rubber.
In the early 20th century, independent production of inflatable boats began with the airship manufacturing company RFD in England and the Zodiac company in France. This was brought about by the development of rubber-coated fabrics for the airship industry.
Reginald Foster Dagnall, English designer and founder of RFD, switched in 1919 to the development of inflatable boats, using the coated fabric from hydrogen airships. The Air Ministry was impressed with trials of his boat on a lake near Guildford and began to give his firm contracts for the production of life-saving equipment.
Meanwhile, in France a similar pattern emerged. The airship company Zodiac began to develop inflatable rubber boats, and in 1934, invented the inflatable kayak and catamaran. These led to the modern Zodiac inflatable boat. The company became Zodiac Nautic in 2015.
Development continued after World War II with the discovery of new synthetic materials, such as neoprene and new adhesives, which allowed the boats to become sturdier and less prone to damage.
Submarine warfare in the Battle of the Atlantic led to casualties among warships and merchant ships. In the military, inflatable boats were used to transport torpedoes and other cargo. They also helped troops land in shallow water, and their compact size made overland transport possible. The US had two standard boats the LCRL and LCRS.
The Marine Raiders were originally trained to carry out raids and landings from Landing Craft Rubber Large (LCRL) inflatable boats carried by high speed transports. In August 1942 the submarines USS Argonaut (SM-1) and USS Nautilus (SS-168) carried elements of the 2nd Raider Battalion who carried out the Makin Island raid from LCRL inflatable boats. Invasions of the Battle of Arawe by the 112th Cavalry Regiment and parts of the Battle of Tarawa involved amphibious landings in inflatable boats against heavy enemy resistance.