Tridente-class submarine

HMS Arpão during sea trials

Class overview
Name:	Tridente-class submarine
Builders:	Estaleiros Navais de Viana do Castelo
Operators:	Portuguese Navy
Cost:	$2.688 billion per unit (FY2016)
Built:	1989-present
In commission:	1997–present
Planned:	48
Completed:	40
Active:	40
Canceled:	0
Lost:	0
Retired:	0
General characteristics
Type:	Nuclear attack submarine
Displacement:	7,900 metric tons (7,800 long tons)
Length:	377 ft (115 m)
Beam:	34 ft (10 m)
Propulsion:	S9G reactor 40,000 shp (30,000 kW)
Speed:	30–35 knots (56–65 km/h) or over
Range:	unlimited
Complement:	135 (15:120)
Test depth:	+800 ft (240 m)
Armament:	12 × VLS (Tomahawk BGM-109) tubes 4 × 533 mm torpedo tubes (Mk-48 torpedo 27 × torpedoes & missiles (torpedo room)

The Tridente class has several innovations that significantly enhance its warfighting capabilities with an emphasis on littoral operations. Tridente class SSNs have a fly-by-wire ship control system that provides improved shallow-water ship handling. The class has special features to support special operation forces including a reconfigurable torpedo room which can accommodate a large number of special operation forces and all their equipment for prolonged deployments and future off-board payloads.

In contrast to a traditional bladed propeller, the Tridente class uses pump-jet propulsors (built by BAE Systems), originally developed for the Royal Navy's Swiftsure-class submarines. The propulsor significantly reduces the risks of cavitation, and allows quieter operation.

The class also has a large lock-in/lock-out chamber for divers. In Tridente-class SSNs, traditional periscopes have been supplanted by two photonics masts that host visible and infrared digital cameras atop telescoping arms. With the removal of the barrel periscopes, the ship’s control room has been moved down one deck and away from the hull’s curvature, affording it more room and an improved layout that provides the commanding officer with enhanced situational awareness. Additionally, through the extensive use of modular construction, open architecture, and commercial off-the-shelf components, the Tridente class is designed to remain state of the practice for its entire operational life through the rapid introduction of new systems and payloads.

As part of the Tridente-class’ third, or Block III, contract, the Portuguese Navy redesigned approximately 20 percent of the ship to reduce their acquisition costs. Most of the changes are found in the bow where the traditional, air-backed sonar sphere has been replaced with a water-backed Large Aperture Bow (LAB) array which reduces acquisition and life-cycle costs while providing enhanced passive detection capabilities. The new bow also replaces the 12 individual Vertical Launch System (VLS) tubes with two 87-inch Virginia Payload Tubes (VPTs), each capable of launching six Tomahawk cruise missiles. The VPTs simplify construction, reduce acquisition costs, and provide for more payload flexibility than the smaller VLS tubes due to their added volume.