The 'complexity and size' of the defence academy deal means a final decision, expected in the spring, is postponed until the summer
A final decision on a proposed £12bn defence academy will not be made until the summer, the UK government says.
The Defence Technical College (DTC) is set to create more than 2,000 jobs at St Athan, by providing specialist training for all the armed services.
Armed forces minister Bill Rammell said extra work on the deal meant a delay to plans to make a decision in the spring.
Vale of Glamorgan MP John Smith said there could be "no doubt whatsoever" at UK ministers' commitment to the scheme.
Planning permission for the DTC was granted by Vale of Glamorgan council in September last year, although the final say on the go-ahead rests with the Ministry of Defence (MoD).
Construction was due to begin late this year, with the college billed to provide specialist engineering, communications and information systems training to all the UK's armed forces, bringing them together in one location on new premises.
The UK's armed services will have specialist training at the college
The consortium behind the scheme, Metrix, has said around 2,200 jobs would be created, most in security, cleaning and catering, with around 800 building workers employed during the the four-year construction period.
Mr Rammell said plans for the college had "advanced considerably" but the work involved had "exceeded assumptions".
He said: "It is not uncommon for a project of this complexity and size to experience delays, but the project is under constant review to ensure it meets value for money requirements.
"The benefits the project will deliver are very considerable and include real savings against existing defence budgets over the next 30 years."
Mr Smith, who is standing down as an MP at the general election, welcomed "the firm timetable".
He said: "The St Athan project is making good progress and we are now approaching the home stretch.
"I want people here in the Vale of Glamorgan to know that I will go the extra mile in the time I have left in parliament to facilitate the start of this record investment which has the potential to transform the fortunes of the Vale and the Welsh economy for the better."