This WHATIF postulates how better communication could have truly crushed Lee’s Day 2 plan.
This WHATIF doesn’t really change the actual situation as it played out on 2 July 1863, it just postulates how a simply order could have re-routed forces and disrupted Longstreet’s left flank attack.
In the actual battle, Sykes’ Fifth Union Corps arrived at Gettysburg about 4PM, just as Longstreet’s two division were beginning their attack. It fell to COL Strong Vincent to accept responsibility and deploy his regiments to Little Round Top to save the Union left flank.
Not long thereafter, probably before 6PM, LTG Slocum’s Sixth Corps arrived from the south along the Baltimore Pike. This means that they were en route during the heaviest of the fighting. WHATIF better communications had allowed Meade to re-direct Sixth Corps path? All they would have had to do was divert off of the Pike and cross the open country slipping past Big Round Top to the SW. They could then have attacked directly into the rear area of Hood’s Division as it was heavily engaged from the wheat field to LRT.
Sandwiched between two Union forces, Hood could have been annihilated. The biggest problem would have been avoiding friendly fire cross-fire casualties as Slocum closed in from the south.
At the end of the day, Sixth Corps would occupy the south-facing arm of the Lazy-Z defensive formation, with Fifth Corps aligned on LRT and assuming the role of reserve corps.