Convoy Fuel Plan with a Loaded Truck
A convoy of three 6×6 trucks must cover 780 km, a distance that includes a 60 km detour around a demolished culvert. Each truck's tank holds 200 litres and, on paper, returns 4 km per litre. Unit standing orders require a 20-litre reserve to be kept in the tank at all times. All three trucks start with 180 litres. A forward refuelling point at km 380 holds 150 litres. The convoy commander must decide whether that stock can be split, whether any truck needs jerrycans, and what to report to battalion. One truck is carrying a bulldozer on a trailer.
1. Using the book fuel figure, how much must each truck draw at km 380, and is the 150-litre stock sufficient?
Read the worked answer
Total fuel needed per truck = 780 ÷ 4 = 195 L.
Fuel state at km 380
- Consumed = 380 ÷ 4 = 95 L
- Remaining in tank = 180 − 95 = 85 L
Requirement for the last 400 km, including the reserve
- 400 ÷ 4 = 100 L to run
- plus 20 L reserve = 120 L needed in the tank on departure
Draw per truck = 120 − 85 = 35 L.
Three trucks = 3 × 35 = 105 L against 150 L held - sufficient, with 45 L spare.
Note it is not sufficient to say '105 < 150, therefore fine'. The reserve is a limit on arrival fuel, not a rounding allowance; the 20 L must be inside the 120 L, which is why the draw is 35 L and not 15 L.
2. The truck carrying the bulldozer actually returns 3 km/L. Recompute the draws and state whether the plan still holds.
Read the worked answer
Recompute the loaded truck.
- Total need = 780 ÷ 3 = 260 L
- Consumed by km 380 = 380 ÷ 3 ≈ 126.7 L
- Remaining in tank = 180 − 126.7 = 53.3 L
- Requirement for the last 400 km = 400 ÷ 3 ≈ 133.3 L, plus 20 L reserve = 153.3 L
- Draw = 153.3 − 53.3 = 100 L
Revised total = 35 + 35 + 100 = 170 L against 150 L held: 20 L short. The plan does not hold.
Options, in order of preference:
- Fill the laden truck to 200 L before departure. It then reaches km 380 with 73.3 L and needs a draw of only 80 L, making the total 35 + 35 + 80 = 150 L - exactly the stock, with zero margin. Workable but brittle.
- Pre-position extra fuel. Send a light vehicle ahead with 50 L, so the plan retains a margin rather than matching stock to requirement exactly.
- Carry jerrycans on the laden truck - but remember the jerrycans consume payload and worsen the 3 km/L figure, so this is the weakest option for a vehicle already towing.
Report to battalion: 20 L shortfall at km 380; recommend option 2 and confirm actual consumption at the first 100 km before committing.
3. Which assumption in this plan is most likely to fail, and what single check would you order first?
Read the worked answer
The weakest assumption is the mileage figure itself. The 4 km/L is a book value for good going; the route includes a 60 km detour around a demolished culvert, which means soft ground, low gear, stops and reversing - precisely the conditions that destroy fuel economy. The laden truck at 3 km/L already shows how far one load can move the number, and a loaded truck on broken ground could go below that.
First check to order: a dip-and-record at km 100. Measure litres actually drawn against kilometres actually covered for each truck, and recompute the expected km/L for the remaining 680 km. That converts an assumed figure into a measured one while there is still 280 km of reach to the refuelling point.
Second-order checks worth naming: confirm the 150 L at km 380 physically exists and is not a paper figure; confirm tank gauges against dips, since every calculation above assumes 180 L is genuinely aboard; and confirm the reserve discipline is actually enforced at the refuelling point, since crews under pressure will 'borrow' the reserve and arrive dry.