Why Is Iran Regretting Using The Metric System?

Because they've lost a Kilo. 

TWZ.Com: One Of Iran’s Most Advanced Wacky Catamaran Warships Sunk In Epic Fury 

The single Kilo class submarine, Iran’s most advanced, which was docked at the base, also appears to have been sunk, and a large scorch mark sits next to where it was tied-up pier-side. U.S. Central Command confirmed it had targeted the “most operational Iranian submarine” in ongoing strikes last night.

In addition to the sinking of the Kilo, the other historic news, also submarine related, is that we now have an active-in-service US Navy Warship, other than the USS Constitution, that has destroyed an enemy warship:

FoxNews: US submarine sinks Iranian warship by torpedo in a first since World War II.

In addition to that milestone, the submarine successfully sinking the Iranian frigate marks the first time since the Falklands War, when the HMS Conqueror sank the ARA General Belgrano, that a nuclear submarine has torpedoed and sank an enemy vessel. 

Meanwhile, In The Red Sea

On Septemebr 27, US Naval forces in the area came under attack from a "complex"  attack from the Houthis.

Stars and Stripes:  Navy ships shoot down ‘complex’ barrage of Houthi missiles and drones in Red Sea, Pentagon says

Navy ships intercepted a Houthi barrage of missiles and drones launched from Yemen at the shipping lanes of the Red Sea, the Pentagon confirmed Friday, while also denying reports that any ships were hit in the attack.

“We did see a complex attack launched from the Houthis that ranged from cruise missiles and [unmanned aerial vehicles],” said Sabrina Singh, deputy press secretary for the Defense Department.

The Iran-backed Houthi claimed Friday to have damaged three U.S. Navy warships in a bombardment of 23 missiles and bomber drones. The Navy destroyers, the Houthis’ military spokesperson said in a televised speech, were targeted as they transited the Bab al-Mandeb Strait in the Red Sea. The Bab al-Mandeb Strait connects the Red Sea to the Gulf of Aden, between Yemen.

Sure would be nice if instead of passively and simply absorbing attacks (with rather spendy anti-missile missiles, not to mention the risk of an enemy weapon getting through and killing or injuring Americans), the rules of engagement were changed to allow the US Navy to proactively engage the launchersand those firing them before the weapons were fired at the ships.  

I daresay some renewed deterrence and an application of Finding Out to the Houthis of the consequences of flinging missiles and drones at the US Navy would be most appropriate at this time and is long overdue.