(CNN) -- Under a blazing sun in early June, a group of pro-Russian rebels in eastern Ukraine were digging amid pine woods near the town of Krazny Liman. Their grizzled commander was a bearded man in his 50s who would not tell us where he was from, but acknowledged that he wasn't local. He was proud to show off his unit's most prized possession -- a truck-mounted anti-aircraft unit that was Russian-made. He told us the weapon had been seized from a Ukrainian base. A few miles away, in the town of Kramatorsk, rebel fighters displayed two combat engineering tanks they said they had seized them from a local factory. Eastern Ukraine has long been a center of weapons production. They had parked one of the tanks next to the town square.
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Rebels have downed Ukrainian planes flying at high altitudes
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A pro-Russian rebel commander shows off anti-aircraft missiles
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The border region with Russia is very porous, unguarded in many places
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Some contend that larger weapons have come into Ukraine from Russia
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Ukrainian
In early June, they began to target @placeholder planes and helicopters, with some success.
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Ukrainian
The pro-Russian rebels had taken control of several @placeholder military depots and bases and stripped them of their weapons.
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The evidence is circumstantial; a great deal of @placeholder military hardware is in poor condition or redundant.
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The @placeholder military alleged the missile had been fired from Russian territory.
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To hold what remained of their territory, the pro-Russian rebels needed to be able to challenge @placeholder dominance of the skies.