This is the US Type D-5 dilatable barrage balloon, hydrogen filled and with an operation height of 7,500ft (termed "low altitude".)
Barrage balloons were basically of two types, ballonet and dilatable. The ballonet type had an interior ballonet or air chamber that permitted the outer hull to maintain shape as the lifting gas condition changed with altitude and temperature. Generally an air scoop employed wind velocity to maitain air pressure within the ballonet. The dilatable type had no seperate air chamber and was entirely filled with the lifting gas. The hull had elastic lacing or cords such that its aerodynamic shape was maitained during expansion and contraction of the gas inside.
During WW2 the US built considerable numbers of both types of balloons. The dilatable type was considered most efficient in regard to design, however, in actual operation the ballonet type proved to be more practical and could be constructed at significantly lower cost. The British shipped a large number of their Mark VII
ballonet type balloons to the US to help with supply shortages.
In 1/700 scale this finely detailed model of the D-5 is just 37mm long and barely 17mm from top to botton of the tail fins. For 1/600 scale thye dimensions are 43mm and 20mm. Three balloons are included in this set.
Each model has a 2mm diameter socket for a mounting rod.