Penicillin an excellent war weapon because it was so hard to synth, not in spite of that

An excellent antiseptic like synthetic gramicidin was cheap to make, fast acting, stable and a very effective bacterial killer.

But as a weapon of war, it lacked the ability to remain secret for very long .

For if one American chemist could quickly synthesize this product of nature, the massed forces of German Chemistry, widely recognized as the best in the world, would make even shorter work of the same task.

By pointed contrast, despite its relatively small molecular weight, a dozen years of dilatory chemistry efforts by some very good biochemists and some big drug companies had failed to crack penicillin's structure.

It thus promised to be something that even the Germans might take a year to synthesize and get into mass production.

And if both the existence of synth penicillin and the success natural penicillin already had had in curing serious domestic infections could remain a secret until the Second Front opened up on the Germans, that year delay would be a fatal delay.

 Because the first the German High Command would have heard of penicillin was the explanation that it was the new secret Allied weapon that by returning more of their troops (and returning them much quicker) to the front was handily winning the manpower war against the Axis.

The only fly in this happy ointment ?

Man never did succeed, not even 75 years later,  in making penicillin as cheaply and as productively as the penicillium's tiny slime factories did.

(Given that Henry Dawson had spent his whole life demonstrating how smart even the smallest of non-pathogenic bacteria could be, I doubt that he would be surprised !)

Unlike the production of nuclear weapons, the production of penicillin remains as it began, something relatively easy to make in any hospital lab and hardly something that can remain 'secret' forever simply due to its overwhelming expense and complexity.....