Types of Diving -- Diving Bells Page 2
In the 19th century, the diving bell concept was put to use for underwater construction. Engineers used compressed air to keep water out of shafts or tunnels being dug underwater. Large airtight chambers called caissons were also used to shelter workers who carried out underwater construction projects such as building bridge foundations.
Diving bells continue to be used today as part of modern diving systems, providing a method of transporting divers to their work sites while under pressure and, once at the site, of supplying breathing gas while the diver works. Smaller diving bells called personnel transfer capsules (PTCs) are used to transfer divers from one place to another -- for example, from a ship to an underwater destination and back -- while maintaining high pressure.