Which country invented the aerial tanker?

The world's first aerial tanker 1923 was born in the United States. 1923 On August 27th, two planes flew in formation over San Diego Bay, California, USA. A hose with a length of 10 meters is hung on the plane flying ahead. The pilot in the back seat of the plane stands up, grabs the drifting hose with his hand and connects it to the fuel tank of his own plane. During the 37-hour flight, the two planes filled each other with 678 gallons of gasoline and lubricant. This is the first aerial refueling test in aviation history. The code name of the first aerial tanker is DH-4m. At this time, the refueling process is completely operated by manpower, and the tanker is higher than the receiver and refuels by the height difference. This refueling method is difficult to be applied in practice. In the mid-1940s, Britain developed the plug cone sleeve refueling equipment, 1949, and the United States developed the telescopic tube refueling equipment, which made aerial refueling enter the practical stage.