Update 1.31 (changelog) was introduced on 11 June 2013. It is most notable for adding Squadrons to the game.

New Vehicles

Aircraft

USA

P-36A
P-36C
XP-50 (premium)
XP-55 (premium)

USSR

Japan

New Premium Level 1 aircraft

USA - Thach's F2A-1 Buffalo

Germany - Marcolin's CR.42CN

USSR - Zhukovsky's I-153-M62

Britain - Tuck's Gladiator Mk II

Japan - Hagiri's A5M4

After your first battle against other players (in case you receive any XP) – You will receive one of these aircraft for the nation you chose. (One free aircraft only)
Choose your first battle carefully!
Second and fifth battle will bring you some bonus XP
Seventh battle will give you 50 000 Silver Lions!

Game Changes

Squadrons

Squadrons are in-game integration of players, designed for joint combat, participation in tournaments and viewing of squadron statistics. The squadrons are designed to unite players under the same tag and title. Members of a Squadron - are brothers in arms who fight side by side, together they share the bitterness of defeat and glory of victory!
You can create your squadron with a unique name, tag and motto. Squadron names can consist of Latin symbols or numbers of 1 to 5 symbols. The maximum number of people in the squadron at the moment is 128. The cost of creating a squadron is 2500 gold eagles.You can monitor the effectiveness of your Squadron in a special record table.
Attention! Squadrons are temporarily unavailable for preliminary registration of existing squadrons. All Squadron features will be available to all players within 2 days after the Update Release.

Integration with Facebook and Twitch.tv

Facebook will allow players to share screenshots, end of the battle windows, display their new rank etc. A functional Twitch.tv account will allow players to share videos of their fights directly in real time.

New Tutorials

The Tutorial’s have been completely redesigned. Now it’s even easier for beginners to learn to shoot, bomb and dogfight!

Play with your friends

Now you can invite your friends for a game of War Thunder with special in-game functionality.
Those signing up will receive an additional 50 eagles at the first entry to the game!
For every friend you get to invite via your account you will receive:
- 50,000 silver lions, when a friend reaches Rank 5 in any country.
- 100 golden eagles when one reaches rank 10 in any country.
- 500 golden eagles when one reaches Rank 20 in any country
- The unique extra crew slot in each country if 10 friends that you have introduced have all reached rank 10.
- As well as additional rewards if a guest buys Eagles!

New maps for Arcade

Top of the World
Arctic - dazzling snowy landscapes and a variety of targets: pillboxes, artillery, armoured columns and ships. You will be engaging the enemy in a dynamic battle over the "top of the world."
Cliffed Coast
Ireland - sharp closely spaced high cliffs - a great place to play cat and mouse. You will perform incredible maneuvers that will help throw off the enemy on your six by creating an obstacle course for him to pursue you.

Zhengzhou - Historical Battles (Custom Battles only at the moment)

April 14, 1944 of the 12th Japanese Army of the Northern Front launched an offensive against Chinese troops of the 1st Military District (BP) in the direction of Zhengzhou, Tsyueshan, breaking through the Chinese defence by armoured vehicles. Thus was the beginning of the Beijing-Hankousskoy operation, a day later they moved toward the 11th Army of the Central Front of the District of Xinyang, on the offensive against the 5th Chinese BP to surround the Chinese group in the valley of the Huai River. participating in this operation in the main areas was 148,000 Japanese soldiers and officers. The attack was successfully completed by May 9. Parts of the two armies joined in the town of Tsyueshan. During the operation, the Japanese had captured the strategically important city of Zhengzhou (April 19) and Luoyang (25 May). In the hands of the Japanese was a large part of the province of Henan and the entire railway line from Beijing to Hankou.

Interface

The new interactive background hangar for your aircraft. Now all your planes are located right on the runway.
Added the display of the cause of death of your aircraft.
The "Save username and password" in the login window is now divided into two separate fields.
Added three new variants of the login window background and loading.
slightly redesigned colour scheme of in-game interface.
Complete redesign of the debriefing panel, it is now more informative and colourful.
Reworked Pilot Card.
Completely changed the tab "Achievements" and "Awards".
The decal application interface has been re-designed to be more user friendly. Now all the decals are in one place.
Game options Menu - added "Community" with the settings for Facebook and Twitch.tv.
Changed the icons indicating the current bonuses and promotions.
Changed the color of the text when displaying events in battle. Now, the message text will be displayed pale blue when shooting down the enemy and pale red - an ally instead of white, as before.

Graphics

Changed the calculation of shadows, increased their effective resolution;
Added effect lens flare;
Added effect of SSAO (approximate global illumination simulation technology) for quality settings;
Improved lighting model for aircraft;
Improved support for 3D Vision;
Improved game performance in the all Higher Settings (except for ATI cards with the old drivers and ATI graphics cards to 4800 series);
Changed calculation and rendering of clouds. Clouds now intersect with the terrain without visual artifacts;
Fixed animation of tailhook hook on the the F4U;
Fixed display of slats on some aircraft;
Fixed display of torpedoes in the hangar.

Sound

New voices for voice commands in English, French, Spanish and Italian added;
New sounds for the new hangar and debriefing window
New voicework for tutorials (Russian and English)

Game

Added air raid siren on airfields;
Added cockpit for dive bomber Pe-2-1;
Fixed behavior of the AI bombers on missions;
Fixed inability to complete the mission Battle of Solomon Islands;
Improved collision detection on contact with the surfaces of the aircraft;
Fixed wandering planes on moving aircraft carriers;
Added modification for the bomber crews of the United States and Britain: splinter-proof vests;
Improved synchronization with the server for aircraft;
Improved movement of ground vehicles in a formation while moving on the roads;
Added additional fuel filling (MW50, GM1, NO2, WM) on the ground;
Improved behavior of bombs, rockets and torpedoes in the air, they now behave more realistically;
Fixed a bug that caused the random movement of a Torpedo after launch.
Configured tension of arrestor wires on aircraft carriers, the hooking has become more realistic;
Fixed a bug which resulted in the aircraft severely shaking and jumping up and down on moving aircraft carriers, which gave various random movement.
Fixed incorrect bomb bounce (when uding delayed detonation on some of the bridges;
Improved calculation of the frictional forces, when braking and taxiing over rough terrain.
Rank of Yak-3 raised from 9 th to 10 th;
Rank of La-7 lowered from 14th to 12th;
Rank of La-5 FN lowered from 11 th to 9 th;
Rank of Ki-49-IIb raised from 7 th to 8 th;
Rank of Ki-49-IIb / late increased from 7 th to 9 th;
Added mountable suspension modification kits for weapons R5 Bf.109G-6, Bf.109G-10, Bf.109K-4;
Ability to mount through modification of motor gun MK 108 Bf.109G-10;
Added MGFFM gun for the following aircraft: Bf-110C4, Do-217E4 (turret version);
Posted bomb armament for the F-86A-5 Sabre, in the form of 2-under-wing 500-pound bombs;
Added bomb load for Do.217N-1 - 8 bombs sc50;
For IL-10 added bomb load of 2-250kg bombs FAB-250;
For the Yak-9P added mountable modification motor gun: NA-23 and H-37 (23 mm and 37 mm, respectively);
For BK-37 cannon added a new ammo rack option - "To engage aerial targets";
Machine gun type 92, type 89, type 97 to change the default ammo racks (part of general purpose bullets replaced by special);
For aircraft, armed with guns and ShVAK Hispano, added options for racks with an increased number of tracers (every second and every third, respectively);
The redesigned mechanism for information conversion rate of weapons in the arcade fighting (the old values are reset to the default value of 400 meters);
Added increase in the spread of shells as increasing the length of the burst of heavy automatic cannon;
Reduced the chance of large-caliber automatic guns jamming when firing long bursts;
Improved visibility of tracers on caliber 7 mm, 12 mm and 20 mm;
Refined ballistics, loss of penetration and damage to the caliber of the bullets and shells 7.5-7.92 mm, 12.7-13 mm and 20-23 mm;
Redesigned high-explosive and fragmentation effect for all shells and bullets;
Improved effect of explosive and incendiary bullets on the aircraft skin;
Fixed position of the effect of the shot on the MiG-9;
Implemented simulation time delay fuses (projectile after charging may take some distance from the trigger and go deep into the design of the aircraft);
Fixed number of rounds to 20-mm cannon Bf-109G10 from 150 to 200;
Fixed a number of shells for the guns of La-7 from 150 to 170 on the trunk;
For LaGG-3 series 35 and 66 to change the amount of cartridges and shells: from 500 to 200 for a machine gun UBS and from 120 to 150 for the gun ShVAK.
Fixed amount of ammunition for the machine guns MG 131 turret on the aircraft Me-410a-1, Me-410a-1 u2, Me-410a-1 u4 from 450 to 500 rounds per gun;
Fixed number of rounds on two foreign exchange guns MG 151/20 on an airplane Me-410a-1 u2 from 230 to 250 rounds per gun;
Changed the number of cartridges on a plane P-40 until you have 240/291/312 rounds per gun;
Fixed turret on the aircraft Ju-87D3/D5/G1/G2, MG17 machine gun replaced by coaxial MG-81 machine guns
Fixed a bug in the aircraft armament Er-2 with turret Lu2B M105 machine gun in the bottom hatch install corrected to collar;
On the MiG-9, MiG-15 NS-37 cannon replaced by Guns N-37D;

Changes in DM

Reworked dynamic damage model of aircraft;
Reworked damage system: Liquid and air cooling;
Refined materials design elements and components, specified strength of the various elements of the design;
Refined work of fire prevention systems on the aircraft (charging neutral gases, self-sealing tanks, etc.);
Reworked system fires, increasing the probability of fire fighting shifted toward higher velocities, the probability of extinction at high speeds enhanced;
Fixed a bug where some of the planes could continue a long flight with no visible damage in the presence of a fire.

Other Changes

Error in Do.217J and Do.217N1 planes description fixed (cannon ammo capacity was wrong)
OS2U plane description error fixed
Error that lead to random positioning of aiming reticule in Historical Battles is fixed

Changes in FM

list of updated FMs here

Smaller updates that came afterwards

13.06.2013

Better performance for multi-core CPU
Some client crashes fixed

19.06.2013

La-5FN/La-7 climb rate fixed
Textures on some planes were improved
Shadows were improved
Performance was improved
Squadron management improved
Landing on the carrier improved (hook work)
New loading screen images added
Blank icons for some awards fixed
Multi-engine planes' DM fixed

14.06.2013

Strengthened frameworks and load-carrying elements for multi-engined aircraft;
Adjusted damage processing for tail elements of multi-engined aircraft;
Player-controlled turret gunners shoot more precise;
Reduced durability of internal modules of ground units (heavy, medium and light tanks and tank-based AA units). Anti-tank aircraft cannons now inflict more damage to ground forces.
15% increased impulse(speed) for missiles RS-132, RS-82, HVAR, RP-3;
20% increased shooting accuracy of missiles;
Missiles warhead power tuned to these perfomance figures (relatively for all rockets depending on caliber):

Heavy missiles, caliber 127-132mm (RS-132,HVAR, RP-3):

Tanks of all types can be destroyed on direct hit
Heavy tanks and heavy SP guns can be destroyed in the distance of 1,5m from the explosion
Medium tanks and medium SP guns can be destroyed in the distance of 2-3m from the explosion
Light tanks and light SP guns can be destroyed in the distance up to 4m from the explosion
Unarmored targets and artillery can be destroyed by fragments in the distance up to 25m.

Medium missiles (for example, RS-82)

Tanks of all types can be destroyed on direct hit only.
Unarmored targets and artillery can be destroyed by fragments in the distance up to 12m.

Improved accuracy of turret machine guns when controlled by player: reduced additional technical scattering when shooting long bursts.

Changes in missions:

[Domination]
- All Domination missions are now less dependable on ground units. Wiping of ground targets in the beginning of a round won't lead to quick victory.
- Mozdok. Respawn points are changed to make this map spacious.
[Ground Strike]
- Khalkin Gol and Stalingrad: Ground forces positions changed.

21.06.2013

Bug in Fw 190D fixed. Aircraft had 600 kg less weight than historically correct.
Separate leaderboard for squadrons added: Arcade Battles, Historical Battles, Full Realistic Battles. Current leaderboards have been wiped.
Several fixes in HB missions
Several game client's crashes fixed

21.06.2013

New economy. Advantages and disadvantages of two previous models have been taken into account

Prices for buying new planes, modifications, specializations reduced
Battle trophies introduced. This is an additional reward that may be received after battle in AB, HB, FRB.
Chance of receiving a battle trophy depends on your performance in battle, time spent in the air and number of players in game session.
After-battle calculation of damage dealt to a plane is changed, now more parameters are taken into account, thus making calculation significantly more precise.
Repair costs for some planes increased. For certain planes repair costs were reduced.
Rewards for actions in battle have not been changed, Which means that a plane with 100% reward ratio in new economy will receive the same reward as a plane with 100% reward ratio in old economy. Reward ratio changed for some planes, some increased, some reduced.

Squadron sorting in leaderboards in HB/FRB fixed.
Number of players in Squadron leaderboards added.
DM for Ki-45 fixed.
Many client crashes issues fixed.
New personal skin for Tempest added.

28.06.2013

Several game client's crashes fixed

01.07.2013

Preparations for Summer in War Thunder very special event

04.07.2013

Fixes for Oculus Rift
New functions for squadrons
10+ game client's crashes fixed
Polish Air Force decal added