|Luke and his wingmen speed over the exhaust port after their original first failed attempt with torpedoes. A 1976 storyboard.|
With the demise of Red Leader, Luke and his team begin their attack run on the Death Star trench. However, as originally scripted and filmed, he, Wedge and Biggs actually made two attack runs- the first attempt proving a failure as Luke uses his targeting computer (and not listening to Ben's advice in his head) to launch his weapons and missing- the torpedoes going astray and detonating near the shaft. Darth Vader and his wingmen are close behind but fail to catch the fast escaping trio, pursuing them instead into space, with Luke (his X-wing fighter slightly damaged) and Biggs pursued by TIEs (Darth chillingly telling his pilots: "Take them") before both shake off their attackers to re-group with Wedge for another assault.
|Luke's missiles go off course in the original conception.|
|TIE fighters descend to attack Blue (Red) Leader. Back then, in mid 1976, there was no plan to give Vader his own unique ship. That came later and evolved in the design process.|
|Luke and his wingmen rush to Red Leader's singular aid. It is unknown if this shot was ever completed.|
At this point in the film's 1976 conception the idea of setting the sequence to a countdown hadn't been properly worked out-most of that ultimate suspense was created in post production by Marcia Lucas and Paul Hirsch's editing, to give the film more excitement-though the opening portion of the X-wing trio's first trench entry was cleverly sequed into the finished sequence (up to Luke's talking to Wedge about the enemy laser tower), the ultimate omission of Red Five's first unsuccessful torpedo attack did not affect the storytelling- indeed, the loss tightened it up and strengthened it, what with the young Luke now not ignoring Ben's ethereal advice and going on to trust his former mentor and his own instincts in the Force.
With ILM effects/model filming of the Death Star trench run going on until Christmas of 1976, in conjunction with the post production editing, it's likely that the majority of the first trench run sequence by Luke was mostly abandoned by that point, with the technicians concentrating on the adjusted finale instead.
Paul Hirsch brief talk: https://www.youtube.com/watch?v=8Fo3UvNtpMs