[336] HMR-161 _HD_, Dec 51; _Cavalry of the Sky_, 175–176. Two of the original 15 HRS-1 aircraft had been damaged in accidents, but one was later restored to action with parts cannibalized from the other. The Marine helicopters of VMO-6 had also been setting records during the last half of 1951 under four commanding officers, Major David W. McFarland (5 April-5 October), Major Allan H. Ringblom (6 October-31 October), Major Edward R. Polgrean (1 November-25 November), and Major Kenneth C. Smedley (26 November-31 January 1952). A total of 1,096 Marine wounded had been flown out during this period, many of whom would otherwise have lost their lives.[337] [337] VMO-6 _HD_, Jun-Dec 51; _Cavalry of the Sky_, 146, 180–181. The supposed vulnerability of the helicopter was whittled down to a myth by VMO-6 experience. Returning from a front line mission with bullet holes was too commonplace for mention, yet the year 1951 passed without a single helicopter pilot being lost to enemy action, even though several aircraft were shot down. The experience of these 12 months also proved anew the wisdom of combining rotary-wing and fixed-wing aircraft in an observation squadron in fairly equal numbers. When it came to reconnaissance and artillery spotting, the nimble little OYs and OEs (both types are light observation planes) were much better suited than the “choppers.” As for close air support, increased Air Force emphasis on an interdiction campaign beyond artillery ranges added to the limitations imposed on Marine requests. Of the 22 strikes requested in December 1951, only five were approved. From the 1st to the 10th, units of the Division along the MLR consisted from left to right of the 1st KMC Regiment, 7th Marines, and 5th Marines. The only major change took place on the 11th, when the 1st Marines relieved the 7th and the latter went into Division reserve. Enemy units were believed to be the 1st, 15th, and 19th (soon relieved by the 47th) NKPA Divisions with an estimated strength of 25,750. Permission was rarely granted by X Corps for Marine raids to cross the EUSAK military limiting line known as Line DUCK, which generally coincided with the line of demarcation. Christmas passed like any other day except for the holiday feast. Nineteen patrols went out on Christmas Eve, two of which had brief fire fights with enemy patrols before returning at dawn. During the day 40 rounds of naval gunfire from the heavy cruiser USS _St. Paul_ were credited with destroying seven enemy bunkers.