This modified 1956 Caterpillar D6 9U was one of two crawlers bought at the late Robert Wilson's sale by collector and former haulage contractor Dave Cooper. It's seen here working at West Cowick with a tool carrier built by Robert Wilson. #caterpillar #caterpillard6 #crawler #crawlertractor #thetractortwitcher #westcowickworkingweekend | The Tractor Twitcher