U2
As an ATC (AirTC) cadet at ESL in the '60's we used to see them all the time and they went up like that when full of gas as well. Relaced later by the RB57F which was like the Canberra with BIG wings.
The U2s used to go north as well and when they reported over Cooktown going Nocom ("Above FL600") you could hear them at MtIsa - it was all 122.1 in those days. They would go someplace then call up over cooktown southbound for ESL some hours later. All OCTA!
The funny (for us) day was when some RAAF type put a slash between the U and the S on the side of the aircraft one day, so it read....U/S AIR FORCE.... One reason why they use "inop"...