LONDON — The Royal Navy has cut plans to build 13 Type 26 frigates to eight and will launch a concept phase to design a new class of lighter warships to fill the gap, the government announced in the strategic defense and security review (SDSR) unveiled Monday.

The review also said the government wouldn't order any Type 26 frigates from BAE Systems until it had "further matured the design."

The defense review is published every five years, mapping out the government's defense and security posture.

Highlights of the SDSR 2015 include a government pledge to increase spending by £12 billion to £178 billion (US $18.2 billion to $270.3 billion), the purchase of nine Boeing P-8 maritime patrol aircraft, and the creation of two new strike brigades by the Army for rapid deployment missions by 2025.

The Ministry of Defence awarded BAE an £859 million demonstration phase contract earlier this year, and the company had been expecting a contract to cut metal on the first of a three-ship Type 26 order penciled in for next year.

MoD sources, who asked not to be named, said the change from 13 to eight Type 26s may be better news than it first appears.

"It's a commitment for eight warships whereas recently there had been speculation the number could be lower. From an industry perspective the new light frigate will enable BAE and others to keep design and engineering teams busy beyond the scaling down of the Type 26 effort, which would probably have started late next year," he said.

"I don't think either us or BAE will be too unhappy if the date for cutting first metal is pushed back to a date likely to be in 2017," they said.

"We still need the inservice date of the first warship to broadly align with the 2023 going out of service of the Type 23 HMS Argyll," said the source.

However, it is a setback and the government has had to announce it is placing an order with BAE for two additional offshore patrol vessels to ensure "continuity of shipbuilding work and additional capability for the Royal Navy in the short-term," the SDSR said.

BAE said in a statement released after the SDSR was announced by Prime Minister David Cameron in Parliament that the , but said the "government's reaffirmed commitment to shipbuilding continuity provides clarity and future opportunities for the group's shipbuilding facilities and workforce in Scotland."

BAE is already building three offshore patrol vessels at its Clyde, Scotland, yards in a £348 million deal awarded to allow the company to bridge the gap between the end of work on two aircraft carriers destined for the Royal Navy starting 2017 and the start of work on the Type 26.

All three of those new warships are in various stages of build, and the first vessel is scheduled to be handed over to the RN in 2017.

The Royal Navy operates four offshore patrol boats on fishery and other duties. Three of these vessels are eventually expected to be sold off, leaving a fleet of six offshore patrol warships.

The Type 26 is a 7,000-ton anti-submarine warfare vessel set to replace the first of 13 Type 23s starting around 2022. The cost of the Type 26 program has never been officially released, but a senior naval officer at the DSEI show in London in September gave a ballpark figure of £12 billion in outturn price for 13 warships during a speech.

MoD sources later said he had rounded up the figure to £12 billion and the real cost was below £11.5 billion.

The government intends to launch a concept study and then design and build a new class of lighter, flexible, general purpose frigates to complement the Type 26, according to the SDSR.

Details are thin and it's unclear whether the new frigate will be based on the same hull as the Type 26 or something completely different.

Originally, the Type 26 was to have operated in a general purpose role as well as its primary ASW mission.

The review said the lighter, more flexible warship would have a better chance of securing export orders for Britain's naval industry.

The government and BAE had pinned great hopes on the Type 26, also known as the Global Combat Ship, becoming an export success but its complexity, size and cost have shrunk the pool of potential buyers to just a handful of countries like Australia, Canada and Germany.

The current plan remains for the Royal Navy to field a 19 strong fleet consisting of six Type 45 air defense destroyers, eight Type 26 anti-submarine frigates and now five general purpose frigates along with a fleet of offshore patrol vessels.

The SDSR held out the possibility additional general purpose frigates could be added to the fleet beyond 2030.

Unveiling the defense review to Parliament on Monday, Prime Minister David Cameron said the new warship would be "more affordable than the Type 26, which will allow us to buy more of them."

A new national shipbuilding strategy is set to be published next year that is aimed at laying the foundations of a modern naval sector.

A £100 million investment is already underway at BAE's two yards on the Clyde to help increase shipbuilding efficiency.

The defense review also said the MoD would buy three logistics ships in addition to the four tankers already being built in South Korea using a design from the British company BMT Defence Services. One of the new aircraft carriers is to be enhanced to support Royal Marines 3 Commando Brigade in amphibious operations.