Three security breaches at Portsmouth naval base were investigated last year, the Government has said.
Information released by Whitehall showed drones and air balloons flying over bases at low-altitude accounted for some of the security breaches at 41 UK military sites last year.
Ministry of Defence (MoD) data for all unauthorised entries in 2015 show one of the Royal Navy’s major bases recorded the most while the RAF’s drone base and army barracks across the country were also affected.
The 44 breaches in 2015 have been investigated by the military police, MoD police or civilian police, according to Defence Minister Mark Lancaster.
But he attempted to play down the security incidents in a written response to MPs, telling them none of the breaches resulted in any “significant ramifications” for defence security.
There have been 135 unauthorised entries to military sites since 2009, according to the MoD, with 2015’s 44 the highest in the period.
The figures show there were eight breaches in 2009, 13 in 2010, 21 in 2011, 12 in 2012, 13 in 2013 and 24 in 2014.
Failed attempts to access the sites without permission are not recorded, Mr Lancaster noted.
He released a list of the sites affected in 2015 following a request from shadow defence secretary Emily Thornberry.
This shows HMNB Portsmouth recorded three incidents and RAF Leeming in North Yorkshire two incidents.
The other 39 sites include HMS Temeraire in Portsmouth, RAF Waddington in Lincolnshire, where Britain’s drone operations are conducted from, HMNB Devonport and RAF Akrotiri in Cyprus.
Mr Lancaster, in his reply to Ms Thornberry, said of the 2015 data: “The figures for unauthorised entries to military bases include drones and air balloon flying at low altitude over military sites but do not include failed attempts at unauthorised access.
“None of these incidents resulted in any significant ramifications for defence security.
“The Ministry of Defence treats all unauthorised entries very seriously.
“They are investigated to a level commensurate with their complexity and impact by military police, MoD police or local constabulary.”