BATON ROUGE - One of the most destructive storms to ever hit the gulf coast has been retroactively upgraded to a category 4 hurricane.

The NOAA announced Wednesday that Betsy, the first hurricane to cause one billion dollars in damage, had been reclassified using modern technology and analytics.

Betsy made landfall in southeast Louisiana in September 1965 and caused turmoil in places like Baton Rouge and New Orleans, where the levees failed and flooded parts of the city. 

In Baton Rouge, the storm wreaked havoc when it engulfed a barge carrying deadly chlorine gas along the Mississippi River. Though residents near the water were ordered to evacuate, the barge was ultimately recovered safely.

The Hurricane Center upgraded Bety from a category 3 to a category 4 as part of a broader revisioning of the 1961 to 1965 hurricane seasons. Taking a second look at decades-old recordings and measurements using newer technology has allowed experts to more accurately measure the strength of older storms like Betsy.