Army units AssistingMarinesCAMP J. J. CARROLL, Vietnam, June 11 (ANF)~~U.S. Army artillerymen in this camp on a high plateau near the Demilitarized Zone have joined U.S. Marines in a demonstration of inter-service cooperation.In this arrangement, the 1st Bn, 40th Arty; 2nd Bn, 94th Arty, and the 1st Bn, 44th Arty, under the administrative control of the Army's I Field Force Vietnam Forward, are providing general support to the 3rd Marine Division.Full Coverage“We can cover nearly 99 per . cent of the province (Quang Tri), from the China Sea to the Laotian border if we have to,” says Lt, Col. Richard C». Trefry, CO, 2nd Bn, 94th Arty.Self-propelled, 175 mm guns are often moved to new positions when there is a tactical change in Marine operations.Observers HelpSoldiers, in this isolated camp zone some 18 miles by bumpy mad from the nearest airfield, get help from Marine forward observers. Marine reconnaissance teams sent into the jungle call back targets to the fire direction control center.Each week Marines from these reconnaissance units visit the fire direction center, to learn how the artillery weapons work.