Sierra Leone Patrol Post No. 1 Tpo - Info?

There is not much doubt about what this cancel reads:



Patrol Post No. 1

I know it is a traveling post office, but I'm wondering if it is a railway cancel, or if it might be a boat?

So far, my Google searches haven't turned up any confirmation. I know that there were at least two railway systems operating in Sierra Leone, the smaller of which had no special postal markings. I inferred from one passing reference that this strike might be a patrol boat, but that seems unlikely. Some relation to the rail system seems far more likely.

Thoughts?

C.

Hmmm... it sounds more military to me, but no answers...

Confirmation of TPO no further info
http://pbbooks.com/cr51.htm

Sierra Leone Patrol Post was a travelling post office of sorts. It operated from Freetown and ran south as far as Kent (about 30 miles). Mail was collected and delivered by a postman on foot. He went to various small villages en route where there were poor roads and no railways. The service began in 1910 and was discontinued in 1931. Only postmark used read PATROL POST No 1. Another reading No 2 was used on the railway in the 1950's

hope this is of interest

John