Simplify the following text for a Grade 4 native English-speaking person.
Original: The Mark 2 has a semi-integral construction , giving it more strength than a Mark 1 in the event of an accident , although a key driver of the changed construction method was to overcome the serious corrosion problem point in the Mark 1 at the base of the body , where it was attached to the underframe .
Simplified: The Mark 2 has more strength than a Mark 1 in the event of an accident .