Complex sentence: Further improvements on the Python-3 lead to the development of Python-4 in mid- 1980s, which had limited "fire-and-forget" ability but added the option for helmet-sight guidance.
Split into simpler sentences: Further improvements on the Python-3 lead to the development of Python-4 in mid- 1980s. The Python-4 had limited "fire-and-forget" ability, and helmet-sight guidance.