Zambia is also land-locked, so shipping stuff in clandestinely means it has to go through another country - which makes it a lot tougher.
Tanzania was not only friendly but allied, although they didn't have a direct rail connection until 1976. The Congo -- Mobutu's Zaire -- was also friendly, although the rail link there started falling apart in the early 1970s.
Note that India and Pakistan took a long time to get their bombs, and they are much larger countries.
Actually, India could have got its first bomb in well under a decade from achieving criticality. They delayed until 1974 for political reasons.
"Can you develop an atomic bomb?" Bhabha assured him that he could and in reply to Nehru's next question about time, he estimated that he would need about a year to do it. ... [Nehru] concluded by saying to Bhabha "Well, don't do it until I tell you to... A few weeks later, on 2 February, Bhabha was asked how long this would take and he responded "about two years I suppose".
That was in 1962, just two years after their first reactor went critical. However, the death of Nehru put atomic weapons development on hold for the next five years; PM Shastri (1962-66) was a Gandhian who hated the whole idea, and then Indira Gandhi took a couple of years of persuading.
So, India didn't start trying to obtain a bomb until late 1967. From then until the first detonation was about six and a half years -- and that's including a year or more lost when their Phoenix plutonium plant developed a leak and shut down. If that hadn't happened, they could have detonated by late 1972 -- start to finish, five years or a bit less.
Also, because of the need for secrecy, India strictly limited the number of scientists and engineers allowed to work on Smiling Buddha. For much of the time there were fewer than 50 of them, and there were never more than 75. Of course thousands of workers and technicians worked on infrastructure, but nonetheless the core group was astonishingly tiny -- less than 1/10 the size of the equivalent group on Manhattan.
And then there's South Africa. They had a shoestring program exploring the possibility of a bomb from 1971, but we're talking enough staff to fit in one room and a budget measured in millions of dollars per year. Not until 1974 did the government decide to seriously pursue building a weapon. By 1977 -- just three years later -- they had a gun-type weapon chassis ready to go, but didn't yet have enough fissile material. They decided to test the chassis anyway, but then backed down in the face of fierce opposition from the Western powers.
If they had started enrichment in 1971 or '72 instead of '74, they could have gone from zero to having a test-ready bomb in 5 or 6 years.
So, 12+ years doesn't seem completely insane. As noted upthread, the major constraint would be keeping the thing secret.
Doug M.
