Due to problems with the design, it had to be extensively redesigned in the 2010s, and a Spanish government budget crisis forced additional delays.

They are oceanic submarines of medium tonnage with the capacity to carry out long duration missions in scenarios far from their base, and to do so stealthily.

[citation needed] The lead boat in the class, the Isaac Peral [es], the first unit in the series, was launched by King Felipe VI and his daughter, Princess Leonor, heir to the throne, on 22 April 2021 at the Cartagena shipyards, entered to service in 2023, after originally being targeted for 2011.

[10] DCNI then proposed a cheaper option called the S-90B, an S-70 Agosta-class submarine with limited improvements, which was rejected by the French but exported to Pakistan.

As part of Plan ALTAMAR, the firm Bazán (later Izar, and then subsequently, the Spanish state-owned Navantia[7]) started on a new design.

The same year Spain started to look again at its requirements, and in 1998 they indicated that they would buy four Scorpènes,[10] optionally with an air-independent propulsion (AIP) system for greater endurance when submerged.

[12] This was soon overtaken by events, as the Armada (Spanish Navy) became more interested in using submarines for power projection than static defensive role.

The plan envisaged the first boat to be delivered in 2011 but government dithering over the company supplying the combat system pushed it back to 2013.

[18] By May 2013, with over US$680 million of the project's US$3 billion budget for the four submarines spent, an overweight issue was discovered and eventually made public.

[21] In September 2014, the overweight issue was reported to have been resolved in design changes and the construction work to be ready to resume in late October 2014.

[31] The ICSC provides set of weapons and sensors of the combat system with an optimal management of the command and control center, allowing to acquire, evaluate and present all the necessary information for the offensive, defensive or intelligence gathering actions at each moment.

[citation needed] The reformator is fed with bioethanol as fuel and oxygen (stored as a liquid in a high pressure cryogenic tank), generating hydrogen and carbon dioxide as subproducts.

[citation needed] The bioethanol-processor also produces a stream of highly concentrated carbon dioxide and other trace gases that are not burned completely during combustion.

[32] A permanent-magnet electric motor moves a fixed propeller of a special design, that doesn't create cavitations at high speed.