I have been making a game about being a uboat "captain" for a couple of months now. It has been very on and of, so don't expect actual "months" of work.
Your character is a native of a small island chain that God forgot. It is a colony of The Crown Dominion (read Great Britain), however this is mostly just in name. The capital has mostly forgotten that these islands exists, and their only presence takes the form of the local Governor and his small cabinet. Lucky for you and the island, they mostly consider their position a early retirement, considering the island a vacation resort.
Being this tiny forgotten island is the Pacific, the island is quite poor. This doesn't bother most people, living the same lives as their forefathers as fishers and traders. There is a strong makeshift culture, with yearly events where teens and young adults race their makeshift vessels made mostly of scraps. The locals are thrifty and local shippers often remark on their weird contraptions.
But oh no! A world war erupts against The Crown Dominion (thats you!) and The Imperial Union (read Germany). However, luckily most people have forgotten abouth this island, it isn't even on most maps, so you are safe from invasion for now. Eager to prove yourself in the eyes of the governor and the world, you aim to make a name for yourself with your new invention, The submarine.
However, most of what you have access to is scraps and random bits and bobs... Your first prototype is no more than a metal barrel, with a handcrank for movement and a rudder for turning. You haven't even gotten to the submersible part yet. No worries though, this craft can still handle scouting, and basically everyone has forgotten that this is a Dominion island, you can get quite close before arousing suspision.
Luckily, your best friend is a engineer, and given some time he'll get around to adding uppgrades. Progression is based on axis, reputation and time. You gain reputation by helping the war effort by scouting, mining, sinking, doing submarine stuff. Reputation allows you to discover new upgrades. However to unlock upgrades, you need to spend time on patrol, first after they have been unlocked may you install it.
This system (should) work well, since it rewards skilled players with higher end upgrades faster, and for beginners who play more slowly and carefully are able to unlock more Quality of Life upgrades. Basically all functions on your submarine take a lot of maintenance and baby sitting, or are just janky. But most of them can be aleviated with upgrades. Take for example your trusty handcrank and rudder, they are obviously mounted at the rear of your submarine, furthest away from the only window... However in the future, you can unlock a helm so you can controll from a better position.
Now, to make this an actual devlog and not a concept log, let me present the first unlockable upgrade (yet atleast). The small engine! Now you don't have electricity and such, so you'll be hand cranking this one as well. Also you don't have a helm or anything yet, so to accelerate more than idle you will have to fiddle with the carborator. That totally won't be stressful in a encounter...
And here is a image of it
