Spain is having to expand its submarine base as £900m vessel is too big for dock

First it was too heavy, then it was too long. Either way Spain’s expensive attempt to modernise its submarine fleet has gone awry – and left Russian diplomats amused.

The Spanish navy has now been forced to dredge and expand its main submarine base to accommodate the latest version of its S-80 Plus flagship vessel.

Problems with the submarine first became apparent in 2013 when it was discovered it would be too heavy to float, necessitating a redesign to make it lighter and spread the weight over an extra 10 metres.

But that means the vessel is now too long to fit into the submarine dock in the Spanish naval base in Cartagena, south-east Spain. The cost of the infrastructure works needed to adapt the dock to the submarines are estimated at €16m (£14m).

The Spanish government will approve in the next few days raising the total additional cost of the new submarine by €17m and taking the total cost to roughly €1bn for each of the four submersibles, practically twice what was initially forecast.

Reading a report of Spain’s submarine problems, Dmitry Polyanskiy, Russia’s deputy ambassador at the UN, tweeted, “an interesting chain of miscalculations. Never imagined this could be possible in a modern navy”.

Spain’s new socialist government has decided to seek the extra funding rather than see the whole project grind to a halt in the autumn. Margarita Robles, the new defence minister, however admitted there had been deficiencies in the project.

The submarine’s construction was first envisaged in 1999 but it was almost 15 years before problems became apparent with its weight . A Spanish official told the Associated Press at the time that someone had put a decimal point in the wrong place, and “nobody paid attention to review the calculations”.

That mistake cost a reported €14m while engineers and consultants figured out that buoyancy could be improved by lengthening the boat.

Reports in Spain say the biggest uncertainty that continues to weigh on the project is its non-nuclear independent air propulsion system (AIP), which could keep the submarine underwater for as long as two weeks.

The Spanish Ministry of Defence has opted for a system capable of producing hydrogen from bioethanol and has commissioned its development to two Spanish firms, Técnicas Reunidas and Abengoa. Military sources have assured the Spanish newspaper El Pais that, after some sound failure, the milestones are being met.

To avoid further delays, it has been foreseen that the AIP will be integrated from the third submersible (the S-83, whose delivery to the navy is scheduled for March 2026), while the first two (with a delivery date of 2022 and 2024) will begin to navigate with diesel propulsion and will incorporate the AIP when the first overhaul is done at the end of the decade.

• This article was amended on 19 July 2018 because an earlier version said in the next few days the Spanish government would approve raising the total additional cost of the new submarine by €1.7m. This has been corrected to €17m.

