Google will tell you the answer is 172.
If you delve further it is the German Army ID number for this now elderly American Sikorsky CH53G helicopter which were originally built in Germany from 1971-5 and are currently undergoing a largescale modernisation programme at the Eurocopter base at Donauwörth near here in Bavarian Swabia.
They are fascinating Goliaths of the Sky. I have never flown in a helicopter but somehow prefer looking at them with my two feet on terra firma.
Lovely sunny walk as she flew over us probably doing a simulated mission on Memmingen Airport as she was on the standard east to west flightpath approach.