Complex sentence: On the evening of 21 August three parties attempting to bomb the German position from the flanks with only moderate success and a planned for the 22nd failed to materialize due to battalion-level misunderstandings.
Split into simpler sentences: On the evening of 21 August an attempt was made to correct the situation by sending three parties to bomb the German position from the flanks but was only moderately successful. An additional attack planned for the 22nd failed to materialize due to battalion-level misunderstandings.