Financially, DW was a success, however, I'd say the reason Sonalyst sims did poorly is because:

A.) They didn't do much to advance the state of the art since Jane's 688i and had poor realism.
B.) They all had a terrible mission editor.
C.) They all had lackluster campaigns that did not change at all based on the player's inputs.
D.) They all had terrible multiplayer, even DW, which came out in 2004.
E.) Because of D, it was easy for the player to quickly become overwhelmed with all the stations that had to be managed, even with autocrew.

What do you base that on? I remember there was talk of official Sonalysts addons for the game, but those never materialized. Thus it stands to reason the game didn't do very well.

The lack of addons doesn't mean it wasn't a success, it just means Sonalysts didn't want to spend the money.

First and foremost, Sonalysts isn't a gaming company; they're a beltway bandit offering analyst services to the US Navy. They probably decided it was better to focus their efforts on their core business than releasing toy games.

there's no doubt visuals are important, not just for financial reasons, but for visualizing player sub interaction, as well as interaction with environment. with the ue4, there is a possibility to see pbr lighting bring to life the akula in stunning fidelity as it breaches the surface, water glistening and dripping off the hull.

with the talk of high fidelity acoustics, this combination can revive the sub sim genre like star citizens revived the space sim genre. and then you'll see hanger ons try to capitalize off the new insurgence.

with a dcs-like vehicle detail system, i wouldn't mind if there's only a single playable sub at first.

I've been hammered by school for a while now, but I'm looking at putting some time into this again. USML has been under active development this whole time and they had a 1.0 release. My priorities have changed a bit since I last worked on this though. Frankly, UE4's 2d rendering is really awful, and getting it to play nice with NetCDF and USML was really hard and I'm not sure it even worked (can't remember). UE4 would give us really nice 3d rendering, but I'm wondering if that even matters that much if the 2d rendering is terible and the interface is clunky. We were also having lots of issues with the size of the world since UE4's physics engine was designed for small worlds and small players. My current plan is to abandon UE4 and build something around USML and SFML. The major tradeoff here is that I abandon all physics and networking code that I got with UE4 for free. At first glance that sounds like a huge tradeoff, but honestly I think those two will be way easier than they might sound (and sounded to me when I started this project). Networking won't need any client-side prediction or latency compensation and physics can be "you touch something you die" with everything modeled as a capsule at first. Eventually I'm hoping for something a little better.

So what are the benefits of ditching Unreal? There are a few. Most of them boil down to "UE4 wasn't meant for naval simulations". The physics engine can't handle large worlds, or the curvature of the earth. 2d rendering is lacking, etc. Bottom line is that I don't think it can do everything I'd like. So the vision now is a multiplayer sub/ship sim with high-fidelity acoustics, an arbitrary number of players per vessel and an unlimited world size. USML does all its math in spherical coordinates, so might as well cash in on that and ditch the concept of a fixed battlefield size. I think it would be neat to let people work together to control areas of an ocean or stage large battles.

Also to be clear, this is the biggest project I've ever attempted (though not by too much) and there's a very good chance it won't be finished. It'll depend a lot on work and school schedules, as well as motivation. Hopefully I'll have something neat to show everybody by the end of this summer.