▁background . ▁This ▁referred ▁to ▁the ▁Mount jo y ▁that ▁broke ▁the ▁bo om ▁across ▁the ▁River ▁Fo yle ▁during ▁the ▁Sie ge ▁of ▁Der ry ▁in ▁ 1 6 8 9 , ▁providing ▁historic ▁symbol ism ▁for ▁union ists . ▁ ▁In ▁Ul ster , ▁the ▁U VF ▁were ▁given ▁instructions ▁for ▁a ▁full ▁test - m obil isation . ▁ ▁The ▁U VF ▁Motor ▁Corps ▁was ▁sum mon ed ▁by ▁the ▁County ▁An trim ▁commander , ▁General ▁Sir ▁William ▁Ada ir , ▁and ▁instruct ed ▁as ▁follows : ▁ ▁This ▁was ▁all ▁part ▁of ▁a ▁" met icul ous " ▁and ▁" el abor ate " ▁plan ▁to ▁ensure ▁that ▁the ▁operation ▁succeeded ; ▁only ▁ 1 2 ▁people ▁knew ▁the ▁full ▁details ▁and ▁reason ▁for ▁the ▁mobil isation ▁of ▁the ▁U VF ▁members . ▁ ▁This ▁was ▁officially ▁only ▁a ▁" test ▁mobil isation ". ▁Captain ▁F . ▁Hall , ▁the ▁military ▁secretary ▁to ▁the ▁U VF ▁recorded ▁details ▁of ▁these ▁plans ▁in ▁a ▁memor and um . ▁These ▁included ▁t apping ▁of ▁the ▁private ▁tele phone ▁line ▁connecting ▁Hollywood ▁Bar ra cks ▁to ▁Exchange , ▁as ▁well ▁as ▁the ▁short - circ uit ing ▁of ▁phone ▁and ▁te legraph ▁w ires ▁into ▁Lar ne ▁after ▁the ▁last ▁train , ▁and ▁the ▁" short ing " ▁of ▁the ▁main ▁rail ▁lines . ▁ ▁On ▁the ▁date ▁of ▁the ▁land ings , ▁U VF ▁members ▁man ned ▁pick ets ▁and ▁pat rol s ▁along ▁the ▁length ▁of ▁the ▁coast ▁road ▁between