The DMO has worked directly with MARIN and through the Dutch Underwater Knowledge Centre (DUKC), which is a network of both companies and knowledge institutes involved in submarine technology, for many years and more recently during the Walrus service life extension programme.

seventies, the Dutch military procurement arm Defence Materiel Organisation (DMO) decided in 2004 that the Walrus Class should undergo a Service Life Extension (SLEP) programme. This means their operational lifetime is extended by 10 years but the programme was to have a limited budget and thus a limited scope. In October 2013 HNLMS Zeeleeuw (sea lion) started her SLEP at the Naval dockyard in Den Helder. With the extra decade, the Walrus Class would then be operational until the next submarine class entered service – expected in 2027. However, these plans could all have come to nothing if the Netherlands decided to abandon its submarine fleet. But meanwhile, in 2013, news eventually came through that the government would continue to invest in the submarine fleet. This coincided with the fact that Captain Ammerlaan got the chance to return to his beloved submarines. Currently,

the first of the fleet to have completed the life extension - HNLMS Zeeleeuw - is under- going sea trials.

As the extension programme was limited, the DMO decided to focus on safety and operational relevance, Captain Ammerlaan explains. “Safety of course is always vital. Here we looked at the hull, quality of the steel – is it still fully rounded, are all the fittings in the right place, is there any corrosion?” And concerning operational relevance one of the periscopes was replaced with an optronics mast, and investments were made in a new combat management system, improved satellite communication and the ability to be able to operate in a network- centric environment. Sonar processes were improved and the torpedo weapons system was upgraded to the MK48 Torpedo Mod 7AT (Advanced Technology).

Optronics mast One major element MARIN and DUKC was involved in was the new optronics mast. “MARIN was asked to calculate the effects of introducing the new mast and its impact on the hydrodynamic behaviour of the boat. This included exami ning the flow of water in the casing (the outer hull) and how this influences manoeuvrability. For example, if all the new masts are up, to what level will the local flow phenomena change? MARIN also looked at the design of the hatch for the periscope. It is preferable to have an opening rather than a hatch because we want to avoid something mechanical, but again, what impact does this have on manoeuvring and on the noise levels. Is a hatch actually needed or could we introduce small ‘spoilers’ to prevent unwanted effects?”

All of the new equipment had to fit into the existing space as well. “In the event we had

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