Analysis: 5 vehicles can transport 50×5=250 soldiers at a time, so it can be transported in 4 batches 1000 soldiers. And because all the soldiers have to arrive at the same time, the walking distance of each batch of soldiers is the same, and the distance by car is the same. After transporting the first batch of soldiers to a certain place on the way, the car needs to transport the other three batches of soldiers with the same distance, and it needs to meet the soldiers who have not been transported on the way back, so it needs to be returned three times and transported three times.

Solution: Suppose that the distance of transporting the first batch of soldiers to a certain place on the way is X kilometers.

x/30×3+(x-x/30×6)÷(30+6)×3 =( 120-x)÷6

The solution is x = 60.

So this marching plan is: transport each group of soldiers by car for 60 kilometers, that is, transport each group of soldiers by car for 2 hours, and then return to transport other groups of soldiers with no load. In this way, four regiments of soldiers *** 1000 can reach the place where the enemy is encircled.