We did target towing with the B.20 after our bombing role ceased with withdrawal from Vietnam in 1971.
The B.20 was fitted with a lug on the underside, just aft of the camera hatch, I think it was. The target (a dayglo coloured net, "banner" we called it) was layed on the runway after we taxyed in by about 1500 ft. The banner had an aluminium "spreader bar", about 6 ft wide I think, with a couple of discs on it to acts as wheels as it was dragged along the R/W. The cable with an explosive shear bolt was then connected to the lug, and the Canberra took off in a fairly steep climb-out.
Out over the ocean, then set up in an orbit to be joined by a 4-ship of Mirages. They would call "in live" off their perch, shooting ball ammunition. Each fighter in the 4 had a colour applied to their rounds - blue, green, black, or magenta.
At "bingo" for the shooters (not for the Canberra, it could stay all day), they would regroup and go home, and we would pull the banner back home. We would line up off the edge of the runway at 1000ft to drop the banner on the grass - the nav would be down the nose and use the bomb button to fire the explosive bolt to release the banner.
The "knuckleheads" would then retrieve the banner, and take back to their squadron to count up the various colours. Simple.
It was always a jape to head back when they were counting and ask "Who was firing blue?". "Well add one more, we got a blue one through the fin". haha
We did these up in Butterworth (Malaysia) too, up twice a year for our squadrons there - that was known as "TUGBUT". Good fun
Hardly a demanding job, but it was better than a desk as we waited for a FJ position.