Submarine HNLMS Zeeleeuw in dry dock. All four boats of the class were modernized between 2013-2020 as part of the CUP (Capability Upkeep Program). New Combat Management Systems and a Super High Frequency (SHF) communication system were installed. The pressure hull was refurbished, as well as the air monitoring/conditioning systems among other improvements.
The initial lifespan of these boats was thought to be around 25 years, however as the class operated mainly in shallow waters the hull was in better condition then originally anticipated. With the CUP the lifespan was raised to 35 years.
With the CUP the four Walrus Class boats can operate to the fullest of their capabilities before being replaced somewhere around the 2027-2031 timeline. - The boats were commissioned between 1990 and 1994.