Steel company Sheffield Forgemasters is set to be nationalised in a £2.6m deal with the Ministry of Defence.
The government said it intends to invest up to £400m in the historic business for "defence-critical plant, equipment and infrastructure" over the next decade.
The 215-year-old manufacturer plays a key role in the UK's nuclear submarine supply chain.
Unions said the move will end years of instability for the firm.
The acquisition, which is subject to a three-week offer period, is due to be completed on 19 August.
Sheffield Forgemasters described it as an "important milestone" for the company, South Yorkshire and UK manufacturing as a whole.
The 10-year investment from the Ministry of Defence (MoD) will be used to modernise the plant and its equipment to support its role as a long-term supplier to UK defence, a spokesperson said.
The Unite union aid it had "waited two years" for the news and described it as a "huge sigh of relief" for steel communities.
Steve Turner, assistant general secretary for manufacturing, said: "It brings to an end years of instability for this historic company, but is also a sign that government is maybe finally waking up to a crisis of its own making. Critical infrastructure industries like steel function better in public hands and advanced economies like our own need to have stable, secure domestic steel production capabilities to protect our national security interests as well as to compete in global markets."
Source: https://www.bbc.com/news/uk-england-south-yorkshire-57997858