With the 50th anniversary of the Six Day War (currently in Day 3) I thought it might be a good time to link this page from 2010:
The Truth about Area 51: Project Have Doughnut and the Israeli connection.

The enormous haul of Soviet bloc equipment from the 6 Day War was probably the greatest technical intelligence coup since World War 2. Much of the gear, tanks for instance, was familiar in the west, but there were some real bonanzas as well. A complete SA2 surface-to-air missile battery was captured intact, for example. This was at a time when the SA2 was in heavy use against American aircraft in Vietnam. Another surprise was the Soviets’ best field artillery piece, the S-23. This had been seen in Red Square parades, but western analysts did not know even its true caliber (180 mm) until the Israelis came up with captured specimens and a large stock of ammunition. Russian anti-tank missiles and surveillance radar were also part of the loot.
Israel’s willingness to share this with the US was one reason for the lifting of the embargo and the eventual decision to provide outright military aid.