To increase your storage space in Delta Force, you will require the safe boxes that come with each season. But there are several steps to complete before you can get your hands on one. This guide will detail how to get the 3×3 safe box in Delta Force.
Delta Force – How to Get the 3×3 Safe Box

To get the 3×3 Safe Box, complete all of the current Season’s Operation Objectives, 2 Collector Contracts, and 2 Fate Contract missions. Plus, you also get to uncover the Season Exclusive Appearance for the 3×3 safe box if you complete all the Collector and Fate missions. Completing the required missions helps unlock the Season Access for the safe box, which allows you to use it for 24 hours.
Each day, you get to pick different missions when it comes to the Collector and Fate Contract missions. This allows more variety in choosing the mission types you want to do. Whichever contract you feel is easier, complete those or refresh the list. You just need to complete 2 contracts each, so it could take an hour or two to get things done. Once completed, check your Collections menu to find the Safe Box.
How to Use and Equip the 3×3 Safe Box

Once in your Collections menu, select the Items tab on top, select the 3×3 Safe Box, then click on Use. If you don’t want to use it right now, you could keep it and use it whenever you want. This item expires after 55 days, so use it up before that. Also, doing this stores the safe box in your inventory, and it won’t be active if you don’t equip it.
To equip the safe box, head back to the main menu, select the Stash tab on top, select the 3×3 Safe Box, and click on Use to equip it for your current run. Once done, you will see an increase of 9 storage slots in your inventory. You can’t use multiple 3×3 safe boxes together; you need to use up your existing safe box, then complete contract missions to get another.
Since Season 6’s arrival in Delta Force, there is a lot more to do in this update than before, like changing servers, unlocking Raptor, and getting the Golden Bird Nest Easter Egg.