A report by the Public Accounts Committee (PAC) says the Ministry of Defence (MoD) needs to plan on plugging skill gaps, with some skill shortages as large as 26%.
The warning came after the National Audit Office disclosed earlier this year that forces had shortages in more than 100 critical trades, including a 23% shortfall in pilots, 26% in intelligence analysts and 17% in engineers.
Overall, at the start of 2018, there were 8,200 fewer trained regulars than needed - a 5.7% shortfall which the MoD does not expect to close before 2022 at the earliest.
The committee said that, so far, the forces had managed by cancelling leave or training to cover the gaps - but this risked damaging morale, leading to more trained personnel leaving the services.
"This approach is not sustainable in the long-term, particularly as the nature of warfare is evolving rapidly, and the department increasingly needs more specialist technical and digital skills to respond to threats to national security," the committee said.
"The department has not developed a coherent plan for closing the existing skill gaps and securing the new skills that it will need."
According to the report, the MoD needs to develop and install a strategy to close the existing skills gaps and secure the new skills that are needed.
There were also calls for 'more innovative approaches' to recruiting personnel and retaining those with 'specialist skills'.
The report said the MoD is also missing its targets for recruiting women, and people from Black, Asian and Minority Ethnic (BAME) communities.
In the 12 months to September 2017, 12.2% of the intake was female, compared to a target of 15%, whilst 9.2% of recruits were from BAME communities, compared to a 10% target.
Meg Hillier MP, Chair of the Committee, said: “The Government’s ‘make do and mend’ approach to staffing its defence commitments cannot continue.
“Muddling through is unsustainable – a point underlined by the fact that twice as many Forces regulars describe morale as ‘low’ than did so at the start of the decade.
“The MoD must ensure the Armed Forces have the skilled personnel they need to tackle established and emerging threats to national security.
“A creative, effective workforce strategy is long overdue but will be vital if the stresses of today are not to become the crises of tomorrow.”
“Recruiting and retaining talent is one of our top priorities and we have a range of schemes, including retention pay for and direct entry into specialist trades and flexible working to make sure we attract and keep the skilled personnel we need.
"The military has enough personnel to meet all its operational requirements, including being active on 25 operations in 30 countries throughout the world. In the past year we have recruited over 13,000 people into the Armed Forces.”