Reserve Stockpile
A Reserve Stockpile is a special Stockpile created by players at any Storage Depot, Seaport, or Aircraft Depot to privately store reservable crates of items, vehicles, crates of vehicles, shippable structures, and crates of shippable structures.
Creation
A reserve stockpile can be created at at any Storage Depot or Seaport with the Create Reserve Stockpile 
button at the bottom of their interface. An access code is randomly generated. It can be viewed with the View Access Code 
button and shared with other players. Anyone that enters a reserve stockpile's code with the Submit Code 
button gets permanent access to it, other players do not have access to it. The stockpile's creator can use the Show/Hide Reserve Stockpile 
buttons to toggle whether people without access can see them in the stockpile list at the top right, view their content, and submit things into them. The dropdown menu in the top right corner of the building's interface shows the list of all stockpiles visible to the player and lets them switch between stockpiles.
A reserve stockpile is specific to a given Storage Depot or Seaport, meaning a player can have a reserve stockpile at one Depot and a different stockpile at another Depot. Each player can create up to 3 reserve stockpiles per Storage Depot or Seaport. Each player can only have access to 5 reserve stockpiles per Storage Depot or Seaport. If a player hits the limit, the only way to be able to access another one there is to have one of the 5 accessible ones deleted.
Only the creator of the reserve stockpile can delete it with the Release Reserve Stockpile 
button, dumping the content into the public stockpile.
The creator of the reserve stockpile can use the "Reset Passcode" 
button to change the code, revoke the access of every players, and set the stockpile to be invisible.
Storage
A Reserve Stockpile allows players to privately store crates of items, vehicles, crates of vehicles, shippable structures, and crates of shippables. Retrieving content from a reserve stockpile is much faster than retrieving content from the public stockpile. A specific amount and type of thing can be transfered from a reserve stockpile to another accessible stockpile in the same building using 
on their icon, selecting Transfer then choosing an amount. Transfers to the Public stockpile do not leave an entry in the Public stockpile logs.
However the storage capability is more limited than public stockpiles, a reserve stockpile can only store:
- 10 of each type of vehicle and shippable structures
- 10 shippable crates of each type of vehicle and shippable structures
- 100 crates of each type of items (300 for materials that are neither Large Materials nor Liquids).
Pressing the View Reserve Stockpile Actions Log button 
at the bottom of the interface opens the Log of the selected Reserve Stockpile. It contains information about recent submissions, retrievals, and transfers from the stockpile.
Reservability
Reserve stockpiles have an additional limitation, only "reservable" vehicles, structures, and crates can be stored:
- A reservable crate will have "reservable" written in orange in its description.
- A reservable vehicle or shippable structure will show a red padlock in the top right of their menu.
Things that are NOT reservable:
- Any crate, vehicle, or shippable structure previously stored in a public stockpile.
- Crates and shippable crates produced through a public queue.
- Crates of materials that have not been retrieved from the Refinery queue with the
Retrieve All as Cratesoption. - Crates of materials that have been unpacked (except Relic Materials).
- Prototype or upgraded-tier vehicles
- Trains and Train Cars, Battle Tanks and Super Tanks
- Individual Emplacements (although note that emplacement crates are reservable)
Shippables crates of normally unreservable vehicles and structures can be reserved (e.g. crate of 3 Construction Vehicles). But they can only be unpacked into the public stockpile.
Time limit
If a reserve stockpile goes unused for more than 50 hours, it is deleted, with all its content dumped into the public stockpile.
The timer of a reserve stockpile is reset if the player submits a crate to it, even one they just retrieved from it. But they can also click the refresh reserve stockpiles button 
at the bottom of the menu to reset the timer on every reserve stockpile they have access to in that particular Seaport/Storage Depot.