CREATE TABLE table_203_587 (id DECIMAL, "country" TEXT, "weapon designation" TEXT, "weapon description" TEXT, "year ( s )  delivered" TEXT, "quantity delivered" DECIMAL)

which country had the largest number of towed guns delivered ?
SELECT "country" FROM table_203_587 GROUP BY "country" ORDER BY SUM("quantity delivered") DESC LIMIT 1
SELECT "country" FROM "table_203_587" GROUP BY "country" ORDER BY SUM("quantity delivered") DESC NULLS LAST LIMIT 1