Complex sentence: In the second subsidiary action of the offensive, at Saint-Julien, the 4th King's sustained more than 400 casualties over a four-day period, the majority, some 374, while supporting the 1/4th Gurkha Rifles on the 27th.
Split into simpler sentences: In the second subsidiary engagement of the offensive, at Saint-Julien, the 4th King's sustained over 400 casualties during a four-day period. The majority, approximately 374, were incurred while supporting the 1/4th Gurkha Rifles on the 27th.