Complex sentence: Starting in the fall of 1963, teams from the involved countries began assembling at the test grounds for the joint operation, one of many in a series of non-nuclear blast tests under the Tripartite Technical Cooperation Program.
Split into simpler sentences: Starting in the fall of 1963, teams from the involved countries began assembling at the test grounds for the joint operation. This test was one in a series of blasts under the Tripartite Technical Cooperation Program.