Are they actually competitive with freight aircraft? Something like an older DC-3 or C-47 can land and takeoff on short, rough airstrips and are used extensively for shipping goods in remote areas of Alaska. They only need a few crew and are very durable. Don't know how the operating costs compare though.
I think the idea for using airships is that you could basically attach any old container underneath it, effectively using it as a flying container crane.
So the airship puts down a container. Now it needs ballast for not launching in the stratosphere with the reduced weight. You could use water because it can be easily pumped into the airship, but water is not everywhere. Now you need a truck to drive enough water to the destination …
I'm not saying it's impossible but its a big hindrance.
Fun Fact: In the late 90s a german startup named Cargolifter tried this idea. They build a small prototype and one the biggest airship hangar in the world. Then they ran out of money. The hangar today is a tropical indoor water park.
All you need is basic weapons to bring a fully laden ship down. Security of the airspace the whole way is very hard to guarantee as those same countries are often places of severe civil unrest.
Tell that to the RAF. When Zeppelins came to bomb London in WWI the RAF went up to meet them. Other than the fact that it's a daunting prospect to take a single little biplane up against a hulking sky mountain armed with maybe a dozen individually manned machine guns the biggest problem is that shooting a dirigible basically does very little.
When you shoot a Hydrogen filled Zeppelin nothing happens. The Hydrogen slowly leaks out, decreasing lift, but that can be compensated for with dropping ballast. Remember that fire requires those three key ingredients: fuel, oxygen, and an ignition source. An ordinary bullet does not provide an ignition source, and it only just barely helps fuel and oxygen mix.
The RAF developed incendiary rounds and, far more importantly, explosive rounds to take down Zeppelins. Having a round explode on the surface of the gas envelope opens up a large hole, causes prompt mixing of hydrogen and oxygen, and provides an ignition source. Most folks aren't going to have such weapons, it would be just as easy for them to acquire an RPG or MANPAD which could take down any aircraft, so the threat isn't exactly increased.
More importantly, Africa is a huge place, and at any given time most of it does not experience ongoing warfare.
I feel like the one thing that probably does make it much easier to hit than an airplane is it's larger size and slower speed (though I'll admit I have no idea what altitudes dirigibles are able to fly at)
Dirigibles can fly at many thousands of feet. At even a thousand feet it's a lot more difficult to hit something in the air with small arms than across an equivalent distance over land (due to bullet drop) unless you have specialized anti-aircraft guns.
At 1000 feet, the drop of a rifle bullet is pretty trivial (a few yards) compared with the size of an airship. Considering how slow they move, I don't think a moderately competent rifleman would have much trouble hitting them.
The higher the angle you shoot, the more energy loss due to gravity. Shooting at 60 degrees is considerably different than 0 degrees, for the same range. That's why AA guns need to be so big, just to get that bullet up there with enough energy left to do some damage.
Going by the press that's the case, but actually most people in Africa live pretty peaceful lives. And nobody's bringing down aircraft with missiles, so an airship would be pretty safe.
Airships were used during WWI, and they evidently can withstand quite a few gunshots. Winds pushing crafts into the ocean were a bigger problem than gunshots.
A gunshot would not take an airship down. It would be like a pinhole compared to the overall volume, and the gas envelope is compartmentalized so at most you would lose the gas in one compartment. At the very worst it would have to make an unplanned landing but could likely stay aloft for hours even with multiple bullet holes.
