Actually, that “HIVA” was using a mix of initials and Roman numerals –
H-4A (16,000 lbs to 85 mph in 72.5-ft); Essex hangar fit (removed from May 1943)

http://books.google.com/books?id=-UT7MDTeKj8C&pg=PA379&lpg=PA379&dq=H-4+catapult&source=bl&ots=HU7iYMBzR9&sig=FiprGhggdKYXBNjutOqnGoGvhvI&hl=en&ei=h13YTZvaJcrB0AG7uvn7Aw&sa=X&oi=book_result&ct=result&resnum=3&ved=0CCYQ6AEwAg#v=onepage&q=H-4%20catapult&f=false

F MK II (10,000 lb to 35 mph) flywheel type aboard CV-2 & CV-3 from 1920s

H MK II (7000 lbs to 70 mph in 55-ft); pre-war Yorktown class & Wasp fit (including hangar catapult)

H-2-1 (11,000 lbs to 70 mph in 73-ft); CVE/CVL fit, late 1943 fit for CV-3 & CV-6

H-4 (3,500-16,000 lbs to 90 mph in 95-ft); Essex class early fit

H-4A (16,000 lbs to 85 mph in 72.5-ft); Essex hangar fit (removed from May 1943)

H-4B (18,000 lbs to 90 mph in 96-ft); Essex class later fit

H-4C (16,000 lbs to 85 mph in 72.5-ft); CVE/CVL fit late war

H-4-1 (28,000 lbs to 90 mph in 150-ft); Midway class early fit

H-5 (16,000 lbs to 90 mph in 96.7-ft); seaplane catapult (all converted to H-4)

H-6 (60,000 lb to 120 mph); seaplane catapult

H-8 (15,000 lb to 120 mph or 62,500 lbs to 70 mph in 190-ft); replaced H-4B & H-4-1 in post-war Essex & Midway class modernizations

H-9 (45,000 lb to 120 mph or 100,000 lbs to 90 mph in 210-ft); for CVA-58 United States, cancelled