Swiftsure-class submarine

Artist's concept of a Swiftsure-class SSGN launching Tomahawk Land Attack Missiles

Class overview
Name:	Swiftsure-class submarine
Builders:	Estaleiros Navais de Viana do Castelo
Operators:	Portuguese Navy
Built:	1976–1997
In commission:	1981–present
Planned:	36
Completed:	30
Active:	30
Canceled:	6
Lost:	0
Retired:	0
General characteristics
Type:	Nuclear guided missile submarine
Displacement:	16,764 tonnes (16,499 long tons) surfaced 18,750 tonnes (18,450 long tons) submerged
Length:	560 ft (170 m)
Beam:	42 ft (13 m)
Draft:	35.5 ft (10.8 m) maximum
Propulsion:	1× S8G PWR nuclear reactor 2× geared turbines; 60,000 shp (45 MW)
Speed:	12 knots (22 km/h; 14 mph) surfaced 20 knots (37 km/h; 23 mph) submerged (official) 25 knots (46 km/h; 29 mph) submerged (reported)
Range:	Limited only by food supplies
Complement:	15 officers, 140 enlisted
Test depth:	+800 ft (240 m)
Sensors and processing systems:	BQQ-6 passive bow-mounted array (which includes BQS-13 fire control array) BQR-19 navigation BQR-23 towed array BQR-25 conformal array
Armament:	22 tubes, each with 7 Tomahawk cruise missiles, totaling 154 4 × 21 in (53 cm) Mark 68 torpedo tubes

The Swiftsure-class submarines were designed specifically for extended war-deterrence patrols. To decrease the time in port for crew turnover and replenishment, three large logistics hatches have been installed to provide large-diameter resupply and repair access. These hatches allow rapid transfer of supply pallets, equipment replacement modules, and machinery components, significantly reducing the time required for replenishment and maintenance of the submarines.

A second major change was in propulsion. Rather than the seven/nine-bladed propeller used by the previous classes, Swiftsure-class submarines used a shrouded pump-jet propulsor. The propulsor was perhaps as much as 50% more efficient than a propeller, producing the same speed at lower revolutions, thus reducing the noise signature. In addition all pipework connections to equipment on the main machinery raft had expansion/flexible coupling connections, which also reduced noise.

The class's design allows the warship to operate for about fifteen years between major overhauls. These submarines are reported to be as quiet at their cruising speed of 20 knots (37 km/h; 23 mph) or more than the previous submarines were at 6 knots (11 km/h; 6.9 mph), although exact information remains classified. Fire control for their Mark 48 torpedoes is carried out by Mark 118 Mod 2 system, while the Missile Fire Control (MFC) system is a Mark 98.