The British Army has been scaled down by more than 20,000, three years ahead of target.
Latest Ministry of Defence (MoD) figures, outlined in the department's monthly personnel report, show there are 81,700 full-time trained servicemen and women in the Army as of June this year, falling from 102,260 in 2010.
The level is below the planned reduction of the regular force to 82,000 by 2018 as part of the Army 2020 restructuring programme, which also seeks to bolster the number of reservists to 30,000.
The MoD said the Army had the "manpower we need at the moment", although the service faced challenges in recruiting.
But former commander Richard Kemp said it showed the plan was "incoherent".
Col Kemp, a commander of British forces in Afghanistan, told the BBC: "To have already made the cuts by 2015, it shows confusion and targets that don't match up ... it doesn't mean it's a good thing.
"The whole plan was to cover the gaps with reservists, but if you've not achieved that then it must mean that we have got deficiencies.
"Not only does that cause us concern about how we govern our people, but it is also the message we are sending to our enemies. That kind of message always shows aggression towards us."
A MoD spokesman said: "This government is committed to an army of 82,000 and the funding is in place to deliver it. We have the manpower we need at the moment and, working with the army, we are taking clear action to keep driving recruitment upwards."
The restructuring plan has previously been branded a ''shambles'' amid low recruitment levels of Army reservists.
By April this year, the trained strength of the volunteer Army Reserve had reached 21,030, up by nearly 1,000 on the same time last year, as a review suggested recruitment had "turned a corner".
Across all branches of the military, including the Royal Navy and Royal Air Force, the trained full-time personnel numbered 143,200 as of last month, the latest figures show.