▁Army , ▁now ▁Army ▁Reserve , ▁of ▁the ▁British ▁Army . ▁As ▁a ▁qualified ▁doctor , ▁he ▁served ▁as ▁a ▁Medical ▁Officer ▁( MO ) ▁in ▁the ▁Royal ▁Army ▁Medical ▁Corps . ▁He ▁achieved ▁the ▁rank ▁of ▁major . ▁ ▁Mac L aren ▁was ▁posted ▁to ▁the ▁Hon ou rable ▁Art illery ▁Company ▁( H AC ) ▁and , ▁in ▁due ▁course , ▁became ▁the ▁Sur geon - M aj or : ▁the ▁Regiment al ▁Medical ▁Officer ▁( R MO ). ▁The ▁term ▁Sur geon - M aj or ▁applied ▁to ▁all ▁the ▁unit ' s ▁R MO s , ▁most ▁of ▁whom ▁were ▁in ▁General ▁Pract ice ▁( GP ), ▁and ▁it ▁was ▁coinc ident al ▁that ▁Major ▁Mac L aren ▁was ▁primarily ▁an ▁occup ational ▁sur geon . ▁Major ▁Mac L aren ▁also ▁served ▁as ▁loc um ▁R MO ▁to ▁the ▁House hold ▁Caval ry ▁Mount ed ▁Regiment , ▁at ▁Kn ights bridge ▁in ▁London . ▁ ▁In ▁addition ▁to ▁serving ▁as ▁an ▁R MO , ▁Major ▁Mac L aren ▁volunte ered ▁for ▁an ▁oper ational ▁tour , ▁in ▁the ▁former ▁Y ug oslav ia , ▁engaged ▁in ▁the ▁field ▁of ▁military ▁medicine , ▁as ▁part ▁of ▁ 1 st ▁Mechan ised ▁Brigade , ▁with ▁case - work ▁based ▁more ▁on ▁occup ational ▁injury ▁and ▁tra uma ▁medicine , ▁rather ▁than ▁disease ▁and ▁gen et ics . ▁ ▁Having ▁served ▁as ▁a ▁member ▁of ▁the ▁Vol unte er ▁Res erves ▁for ▁more ▁than ▁a ▁de cade , ▁Major ▁Mac L aren