The ATACMS is meant to be a tactical missile system, so the range advantage of the Tomahawk doesn’t count.
And being a ballistic missile, it goes several times faster than the Harpoon and Tomahawk.
http://www.military-today.com/missiles/atacms.htm
Ok from your link:
“This class of weapon is thus widely referred to as a “quasi-ballistic missile”, though the US Army has also referred to the ATACMS as a “maneuvering missile”.”
Given it’s guided on the terminal path and does not actually reach sub-orbit I very much doubt it reaches the terminal speed of 5000 m/s that a ballistic missile reaches. Though it may be faster than a harpoon’s unclassified 240 m/s in some way - since it’s planned terminal speed isn’t listed, ballistic terminal speed is dependent upon altitude obtained, and reduced by any drag introduced through terminal maneuvering - it’s impossible to determine the true difference.
I still see little advantage to investing in a completely new system when the harpoon is already being upgraded to double it’s distance to 134 nm and the tomahawk provides as accurate a delivery at a range of 800-1500 nm dependent on the variant. The Tomahawk does take time to get on target that I’ll give you and therefore is not likely responsive enough to tactical field requirements.
The harpoon on the other hand is a proven tactical weapon that is already available in canister usage - including coastal batteries with a booster, has multiple delivery profiles including a pop-up, and therefore likely easier to convert - in fact it could very easily be programmed to provide a ballistic pattern if that is truly desired.
I guess I’m just having a hard time understanding what the true advantage is given it isn’t a true ballistic speed missile. Doesn’t mean it’s not a good system...long as package is delivered down range, on target, on time.