Complex sentence: The New Zealand advance was obstructed by uncut barbed wire on the Wallemolen spur; the creeping barrage was very thin, as some guns were bogged and others had been knocked out by German artillery.
Split into simpler sentences: The New Zealand advance began poorly as the barbed wire on the Wallemolen spur was undamaged. The creeping barrage was also very thin, as some guns were bogged and others had been knocked out by German artillery.