For a small stream of deliveries, perhaps. And the costs and risks of loss would seem to be fairly linear with an aircraft strategy. The tunnel has large start

For a small stream of deliveries, perhaps. And the costs and risks of loss would seem to be fairly linear with an aircraft strategy. The tunnel has large start-up costs but then tiny marginal costs for bulk transport. Beyond a certain expected lifetime, it'd surely dominate aerial costs/risks for cost-effectiveness. Subs are probably somewhere in-between.