The armed forces are struggling to recruit key medical staff to serve in combat zones, Ministry of Defence officials have said.
Most British soldiers are based in Helmand province
The number of anaesthetists available to the military is currently 48 - but the recommended level is 97.
Emergency nurses, intensive care nurses and other critical care specialists are also needed.
However, officials said the effectiveness of treatment in the field was not being affected.
One official said: "We are struggling to get to the numbers we might need at the worst-case scenario."
He said the armed forces were having difficulty recruiting because of competition from other employers.
"What I'm saying is that we are trying to recruit and retain in a competitive market in the NHS and private sector, and indeed internationally."
He stressed that treatment in the field was not being hampered and that the shortage was not a major concern among troops.
The correct level of medical care was being provided with the use of reservists to plug gaps, the official said.
But he warned that the practice could not go on forever and a long term solution was needed.
"These aren't regulars. What we are doing is providing... reservists," he said.
"And again, that's not a resource we can continue to use for ever and ever.
"One of the things we are going to have to do is to innovate and use other techniques within the NHS to get people interested in going to Afghanistan."
The MoD is currently in the process of reviewing its recommended levels for medical staff - figures which have not been altered since the end of the Cold War.
Staff levels have risen slightly over recent years and the number of anaesthetists available is said to be up from just 22 in 2002.
Military chiefs also defended the practice of treating injured soldiers in NHS hospitals once they were returned to Britain, rather than at dedicated military sites.
They said military-only hospitals were not desirable from a medical or financial point of view.