The British Mandatory government enforced a ban not only on Jews entering the country, but also on Jews acquiring weapons or manufacturing arms under the penalty of death. 

Where was Israel to acquire weapons to defend herself? There were risky efforts to smuggle in weaponry and clandestine production in Israel. But the production that was done locally was neither the volume nor the dimension that Israel required. But Jewish innovation which was the hallmark of the War of Independence met this challenge as well.