A Ukrainian soldier examines a fragment of a Russian Air Force jet after a battle earlier this year at the village of Kolonshchyna, Ukraine. Ukraine has shot down 55 Russian planes during the nearly seven-month conflict, precluding Moscow from achieving air superiority, the top U.S. Air Force commander for Europe said Monday. But Ukraine’s small air force lacks the capability to seize control, creating a situation in which the two sides are embroiled in a prolonged casualty-producing struggle on the ground, according to Gen. James Hecker , who commands the U.S. Air Force in Europe and Africa.

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