Complex sentence: Ketchum p.110 Magaw ordered the Frigates to be fired upon and both British ships were badly damaged by the guns from Fort Lee and Fort Washington because they could not elevate their own guns to the height of the American positions.
Split into simpler sentences: Ketchum p.110 Magaw ordered an attack on the frigates and both British ships were badly damaged by the guns from Fort Lee and Fort Washington. The frigates could not respond because they could not elevate their own guns to the height of the American positions.