Talk:38cm Quadruple Gun Mount Kai/@comment-30534142-20170907175745

After looking into the story of the Richelieu and the book "French Battleships : 1922-1956" by Robert Dumas and John Jordan, i think i've guessed why this gun has an increased accuracy and medium range.

After its refit in the US in 43, Richelieu received a surface surveillance radar (SF) and an air surveillance radar (SA-2) but the US navy refused to give her a GFCS radar.

However when she joined the British Home Fleet at Scapa Flow in early 44, she was fitted with a Type 284 P4 fire control radar for her main guns. It had an effective detection range of 22 km up to over 30 km in good weather conditions (this type of radar helped the Duke of York to detect and sink the Scharnhorst despite poor weather conditions).

So the stats of this gun may reflect the use of that British radar.

Also Richelieu was later equipped with several others radars at Casablanca in late 44, such as a Type 281B air surveillance radar, a SG-1 surface surveillance radar, Type 285P fire control radars with two ABU (auto barrage units) for anti-aircraft barrage fire for the 152mm secondary guns and a jammer against German wire-guided bombs.

In May 45, Richelieu took advantage of a pause in operations to investigate further her excessive dispersion issue. Firing tests revealed that when firing both guns of the same "half-turret" in salvo, if the first hit the target the other was short or over. The dispersion was measured at ~450 m at ranges of 16-25 km (comparable figures for the Queen Elizabeth was ~250 m). New firing trials were made using only a single gun and the dispersion was then measured at ~270 meters (close to the British values).

Since they didn't really figured what caused such a huge  difference in   dispersion when firing both guns in the "half-turret", they decided to only fire one gun from each "half-turret" from the time being (instead of firing 1-2 and 3-4, they'll fire 1-3 and 2-4) until a fix was found. This issue was resolved only postwar in 48, when they figured that the close proximity of the barrels caused a "wake effect" between the shells when fired in salvo.

By adding delay coils (a 0.060 s delay = 50 meters between the shells) to the central guns, the dispersion was reduced by over 40% and Richelieu was now able to fire her "hal-turret" in salvo without worry.

Sources : https://books.google.fr/books?id=YnS9AwAAQBAJ&pg=PA189&lpg=PA189&dq=RADAR+TYPE+284P&source=bl&ots=BT3xkNuASb&sig=u1slsS9AIh7bc7IVDlyXH61I420&hl=fr&sa=X&ved=0ahUKEwicwvTB-pLWAhWHthoKHa7lBZwQ6AEIUjAH#v=onepage&q=RADAR%20TYPE%20284P&f=false