Approximately 69 US Navy PT boats were lost during WWII; discounting LTjg Kennedy's PT-109 which was cut in half by an Imperial Destroyer, the majority of PTs were destroyed by strafing/bombing aircraft. About 11 US Navy PCFs (Patrol Craft Fast), known as Swift Boats, were totally lost during the war. Many Swift's were sunk; However, being constructed from ALUMINUM allowed them to be raised, repaired, and returned to service. This was in contrast to the WWII PT boats which were built of WOOD; and not (willingly) salvagable when damaged. 1. PCF-4 was sunk by a mine. 2. PCF-5, 9, 14, 20, 70, 76, and 77 sank in storms. 3. PCF-41 & 43 were sunk in battle with shore based communist units. 4. PCF-19 was destroyed during a running gun battle with a North Vietnamese helicopter.
The North Vietnamese Navy had Patrol Torpedo Boats; the South Vietnamese Navy countered with (US) Swift Boats.
USN ships of WWII were built of steel; USN PT Boats were built of WOOD. USN ships of WWII also fought in the Vietnam War; USN Swift Boats during the Vietnam War were built of ALUMINUM.
The US Navy's "Riverine Force" in the Vietnam War. The riverine force operated Monitors, Alpha boats, PBRs, and Swift Boats.
A little over 600 wooden WWII PT boats were built; and approximately 9 exist today, on display and/or under-going restoration in various places thru-out the US. These 77 & 80 foot boats were built by Elco and Higgins companies during WWII. Elco built nearly 400 of them, and Higgins built close to 200 of these craft. Nearly 200 Aluminum Vietnam War Swift Boats (officially designated PCF-Patrol Craft Fast) were constructed during the Vietnam war, commencing about 1965. Two are known to exist today for display purposes: one at the National Museum for the US Navy in Washington DC (East Coast) and the other Swift Boat is on an active US Navy base in Coronado CA (West Coast). All of the Swift Boats (PCF's) were built by the Seward Boat Company of Louisiana.
Traditionally it was vessels under 200 feet long. Vietnam Riverine Boats (Brown Water Navy) were all considered boats; Swift Boats (PCF-Patrol Craft Fast), PBR's (Patrol Boat River), Monitors (River Battleships), and Alpha Boats (ASPB-Assault Support Patrol Boats). Blue Water Naval vessels were Frigates, Destroyers, Cruisers, etc.
If you are meaning to U-boats as in World War two? Than U-boats certainly mean "Underwater Boats"
At least 2, possibly 3 companies manufactured the wooden PT boats of WW2. Consequently their lengths varied in size, and so did their complement of crewmen. The average WWII PT boat was manned by about 2 or 3 officers and 12 to 14 crewmen. The Vietnam War Swift Boats (officially designated PCF-Patrol Craft Fast) are alot easier to address: only one company made them; Seward's out of Louisania. These were 50 footers, and all aluminum built; manned by 1 officer and 5 crewmen.
Of course you should have specified which nation? Because the South Viet army may have had more boats than their navy. But although it's been said that the US Army during WWII had more boats than the US Navy did in WWII, the USN in Vietnam probably had more riverine boats than the USA did, for the simple reason USN had: Alpha Boats (ASPB-Assault Support Patrol Boats), PBRs (Patrol Boat River), Swift Boats (PCF-Patrol Craft Fast), ATCs (Armored Troop Carriers), and Monitors (Riverine Battleships armed with 105mm cannons). And the USA basically supplied the men (infantrymen) to be landed and the helicopters.
If you are meaning to U-boats as in World War two? Than U-boats certainly mean "Underwater Boats"
South Vietnam; although there were incidents along the NORTH Vietnamese coastline at, around, near, and above the 17th parallel (DMZ) involving US "Nasty Boats"; and in the Gulf of Tonkin. Nasty boats were built in northern Europe for the US, and looked very much like the wooden WW2 PT boats. These were pre-Swift Boat & PBR & Brown Water Navy days (Before 1965).
Subs are often referred to as boats.
Some people say 17, but the most reliable source I've seen said 15