A month ago the Dutch navy retired the first of its four Walrus-class submarines. The retired sub, the Walrus, had been in service for 31 years and spent 3,000 days at sea. The Walrus-Class boats were designed to service for 25 years but have proved sturdier than expected. This extended service life was helped by the fact that these subs spent most of their time in calmer coastal waters that put less stress on the hull.
The retired boat will become a source of spare parts for the other three subs. These three boats entered service in 1990, 1993 and 1994. The Dutch developed a surveillance technique for these boats that enabled one to remain submerged for 46 days while traveling at 16 kilometers an hour at periscope depth observing its surroundings while taking photos or videos as needed. Along with the periscope was the snorkel device which brought fresh air into the sub to replace the air fouled by the diesel-electric engine and the activities of the 52 sailors who comprise the crew. The 1993 and 1994 subs were upgraded so that they could remain in service until the mid-2030s. This is when the first two replacement subs will be available. The other two will follow by the late 2030s. The new subs will have the AIP (Air Independent Propulsion) system that enables diesel-electric subs to remain submerged for weeks, or even months, at a time. The new subs will require a smaller crew of about 40 or fewer sailors that will operate a more automated submarine equipped with modern sensors and electronics. The Netherlands government will decide by 2024 who will build the successor of the diesel-electric attack submarines to replace the Walrus-class subs.
Three firms are offering proposals to build the new subs. These firms included the French Naval Group, the Dutch-Swedish firm Saab Kockums and the German ThyssenKrupp Marine Systems. It is uncertain what the new subs will cost. Estimates range from $700 million to $1.2 billion each.
The original 2014 plan was to have the first new sub ready for service by 2028. That proved to be unrealistic. Selecting the firm that would build the new sub was to have been taken care of by 2024. That is also considered unlikely. The new plan is to have the first two of four new subs operational by 2037. That gives the winning bidder about ten years to deliver the first subs.
The Walrus class boats were 2,400-ton vessels with a crew of 52 armed with four 533mm (21 inch) torpedo tubes and 20 torpedoes onboard. Other armament includes several machine-guns that can be brought to the deck and used against threats.
Max surface speed is 24 kilometers an hour while it is 37 when submerged. There is a surface-search radar, for use when surfaced, that has a range of nine kilometers. When submerged the passive (listen only) sonar is used that can detect surface ships more than nine kilometers away. Detecting other submerged subs depends on what type of sub is out there. Nuclear subs are louder than diesel-electric boats and submerged subs using AIP are even quieter.
The replacement subs are expected to exceed the capabilities of the Walrus-class boats. How much better the new boats will be dependent on who wins the bidding and what kind of sub they deliver.