It’s Easier to Rebuild
(Source: Swedish Armed Forces Ministry FMV; issued March 12, 2019)
(Unofficial translation by
FMV is currently modernizing two submarines in the Gotland class. They are being extended by two meters and many systems are replaced -- among other things, the control and monitoring system is based on the latest digital technology.

First, the boat is cut in the middle, then she is extended by two meters to make the new technology fit. The cut facilitates assembly work, but it is still a complex job to modernize a 25-year-old submarine.

After 25 years of operation, it was time to take a holistic approach and pass a new eye over the two submarines in the Gotland class. Systems and equipment that are obsolete and are considered difficult to keep in operation during the remaining life are upgraded or replaced.

“It is a very extensive work. It is the most comprehensive modernization that has been done on Swedish submarines. We extend by two meters and we convert many systems on board to newer generations. Not only the management and sensor systems, but also the ship systems,” says Andreas Olsson, sub-project leader ship system for the modernization project at FMV.

Several systems installed on the Gotland submarines are the same as those that will be installed on the two new A26 submarines that FMV will deliver to the Armed Forces. The Stirling engines are an example, but there are also passive and active sonars, connection systems and line support systems. And also the new equipment which replaces the old periscope.

From periscope to camcorder

“Simply put, it can be said that the optronic mast is a video camera with many features. You can look at the screens directly and afterwards you can analyze the moving material on a separate console after you have taken down the mast again, under the surface.”

When the crew wants to track the surface, both for safety and for the tactical use of the boat, you send up the mast for a short time, collect the image material and then analyze them afterwards.

The air-independent Stirling engine has been in the Swedish submarines for 30 years. The basic principle is still the same, but around it has happened a lot.

“We have upgraded it with digital control system, a new generator and better recycling of the residual heat in the exhaust to produce hot water for the crew’s comfort on board,” says Andreas Olsson.

Integration is crucial

“I usually say that it is always more difficult to modernize boats than to build new ones. But modernization is what we do, we are rebuilding old and introducing new technology. And it is a great challenge to take care of the old boat with the new systems.”

On board the submarine there are a variety of systems, such as ship systems that produce compressed air, cooling and hydraulics and which supply many other systems on board. There are both open systems and secret systems and the systems talk to each other.

“The biggest challenge is the integration of all systems. That we switch to digital monitoring systems and that the systems are dependent on each other makes the integration crucial,” says Andreas Olsson.

Three steps ensure quality

FMV's design requirements are verified early in the process by checking drawings, specifications and more. After the systems have been installed on board, the verification takes place in two steps. Partly that they are installed as it is intended purely physically, some performance requirements that can be tested at quay. And finally, verification at sea with the conditions prevailing there and then tested how the submarine works as a whole.

The first of the two modified Gotland submarines is now conducting test tours where FMV ensures that the subsystems and submarine meet the specification agreed with the supplier, but also that the submarine is tested in its tactical utilization, including torpedo firing and submarine hunting together with other units. Then, you really test the submarine and see that it works as it is supposed to.


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