MIL-PRF-44035 Refrigeration Units, Electric, 4000 Btu For Refrigerator-Container, Field, 8 Feet By 8 Feet By 10 FeetThis document covers one type and size of insulated, electric refrigeration unit having a capacity of 4000 British thermal units \(Btu\) per hour and used with an 8 foot by 8 foot by 10 foot refrigerator-container \(see 6.1\).