The key to U.S. success is to suppress the Lafettes. I've seen matches where all the snipers were picking hapless Lafette gunners as soon as the gun was manned, if the mortars, destroyers, or LC machine guns didn't get them first - such matches ended up at the last flags (though with a narrow German victory).
Then, one day even I managed to get 60+ kills on the Lafette, and the U.S. struggled to cap even one WN. Only sporadic mortar fire, no sniping, and LC gunners stopped even trying after I got a couple of them. Very little attempts to advance at the flanks or to try get under the guns - just one mad zergrush to the centre WN where nearly all German emplacements have a clear shot. BRAAAP BRAAAP