WASHINGTON — The Pentagon is racing to boost its production of artillery shells by 500 percent within two years, pushing conventional ammunition production to levels not seen since the Korean War as it invests billions of dollars to make up for shortfalls caused by the war in Ukraine and to build up stockpiles for future conflicts. The effort, which will involve expanding factories and bringing in new producers, is part of “the most aggressive modernization effort in nearly 40 years” for the U.S. defense industrial base, according to an Army report. The new investment in artillery production is in part...