¶ Technical Systems of the F-35 Lightning II

The F-35 Lightning II is the most complex and expensive weapon system in the history of military aviation. As a fifth-generation fighter jet, it embodies a fundamental paradigm shift: away from pure kinematic superiority toward information dominance and spectral superiority [1]. This article documents the ten central technical systems of the F-35 based on verified original sources.

¶ 1. Platform Variants

The F-35 is produced in three variants based on a common basic design, yet differing significantly in their construction. Contrary to frequent claims, the actual commonality between the variants is only around 20% shared structural components [2].

¶ F-35A (CTOL -- Conventional Takeoff and Landing)

The F-35A is the primary variant of the US Air Force and the export model for international partners, including Switzerland. It is designed for conventional takeoff and landing on paved runways.

Parameter	Value
Maximum Speed	Mach 1.6
Combat Radius	>1,093 km (590 nm)
Service Ceiling	>15,240 m (50,000 ft)
g-Limit	+9.0/-3.0 g
Internal Fuel Capacity	8,278 kg (18,250 lbs)
Empty Weight	approx. 13,290 kg

Source: USAF Fact Sheet F-35A [3], Lockheed Martin F-35 Brochure [4]

¶ F-35B (STOVL -- Short Takeoff and Vertical Landing)

The F-35B is the variant of the US Marine Corps and the Royal Air Force. It features the Rolls-Royce LiftFan system and a swiveling nozzle that enable short takeoff and vertical landing.

Parameter	Value
Combat Radius	>833 km (450 nm)
Vertical Thrust	>18,000 kg (combined)
g-Limit	+7.0 g
Special Feature	Smaller weapon bays than F-35A/C

¶ F-35C (CV -- Carrier Variant)

The F-35C is the carrier variant of the US Navy with a reinforced airframe, tailhook, and folding wings for aircraft carrier operations.

Parameter	Value
Combat Radius	>1,111 km (600 nm)
Wingspan	13.1 m (43 ft) -- larger than A/B
g-Limit	+7.5 g
Special Feature	Reinforced landing gear structure, larger wing area

¶ Production Numbers

As of the end of 2024, over 1,000 F-35s have been delivered to international users. The annual production rate is approximately 150 aircraft, with a target of 156 per year [5].

¶ 2. Propulsion -- Pratt & Whitney F135

The Pratt & Whitney F135 is the most powerful fighter jet engine ever to enter serial production. It exists in three sub-variants [6]:

F135-PW-100: Standard variant for the F-35A and basis for the F-35C (the version Switzerland is procuring)
F135-PW-400: Marinized variant for the carrier variant F-35C
F135-PW-600: STOVL variant with coupling to the Rolls-Royce LiftFan for the F-35B

¶ Performance Data

Parameter	Value
Dry Thrust	approx. 128 kN (28,000 lbf)
Afterburner Thrust	approx. 191 kN (43,000 lbf)
Engine Length	approx. 5.59 m (220 inches)
Inlet Diameter	approx. 1.09 m (43 inches)
Architecture	Three-stage fan, six-stage high-pressure compressor, annular combustor
Maintenance Concept	6 hand tools for all Line Replaceable Components

Sources: P&W F135 Fast Facts [7], P&W F135 Characteristics [8]

¶ Fleet Status

Over 1,300 engines have been delivered and have collectively accumulated more than 1 million flight hours [6].

¶ Engine Core Upgrade (ECU)

The ECU modernizes the engine core and offers [9]:

+25% more electrical power and cooling capacity
Double thermal management capacity (critical for Block 4 avionics)
Full retrofittability for all three F-35 variants
Critical Design Review (CDR): mid-2025
First test run: 2026, planned entry into service: 2029

The ECU contract amounts to 1.31 billion USD [10].

¶ AETP and NGAP

The Adaptive Engine Transition Program (AETP) with the demonstrators XA100 (GE) and XA101 (P&W) was not pursued further for the F-35, as the adaptive engines only fit the F-35A but not the B and C variants [11]. Instead, the AETP technology is flowing into the Next Generation Advanced Propulsion (NGAP) program for the F-47 (NGAD) with a total volume of 7 billion USD [12].

¶ 3. Avionics Suite

The avionics of the F-35 consist of four tightly integrated main systems that are linked by a central fusion engine into a unified tactical picture [13].

¶ AN/APG-81 AESA Radar

Developed by Northrop Grumman, the AN/APG-81 is a third-generation Active Electronically Scanned Array (AESA) with approximately 1,676 transmit/receive modules (TRMs) on a GaAs (gallium arsenide) basis [14].

Operating Modes:

Air-to-Air: Long-range detection, Track-While-Scan, multiple target acquisition
Air-to-Ground: Synthetic Aperture Radar (SAR), Ground Moving Target Indication (GMTI)
Electronic Warfare: Directed RF energy for jamming enemy emitters
LPI (Low Probability of Intercept): Frequency agility and power management

The system received the David Packard Award for outstanding acquisition performance in 2010 [14].

¶ AN/AAQ-37 EO-DAS (Distributed Aperture System)

Six MWIR sensors (Medium-Wave Infrared) distributed across the aircraft provide complete 360-degree infrared coverage [15]. Functions include:

Missile warning and tracking
IRST (Infrared Search and Track)
Ballistic missile tracking up to 1,300 km range
Night navigation and landing

Starting from Lot 15, the original Northrop Grumman system is being replaced by a next-gen version from RTX/Raytheon [16].

¶ AN/AAQ-40 EOTS (Electro-Optical Targeting System)

Developed by Lockheed Martin, the EOTS is the world's first conformally integrated electro-optical targeting system [17]. It combines:

Forward-Looking Infrared (FLIR)
Infrared Search and Track (IRST)
Laser Designator and Laser Spot Tracker
NAVFLIR (Navigation FLIR)

The Advanced EOTS upgrade (starting with Block 4) introduces SWIR sensors (Short-Wave Infrared) and HDTV resolution [18].

¶ AN/ASQ-242 CNI Suite

The Communications, Navigation and Identification (CNI) suite from Northrop Grumman integrates over 27 avionics functions into a Software-Defined Radio system [19]. It includes:

MADL (Multifunction Advanced Data Link)
Link-16 tactical data link
IFF (Identification Friend or Foe)
Precision navigation (GPS/INS)
Voice and data communications

¶ 4. Radar Systems -- AN/APG-81 vs. AN/APG-85

¶ The Technology Leap: GaAs to GaN

The planned transition from the AN/APG-81 to the AN/APG-85 marks a fundamental technology change in the semiconductor basis of the transmit/receive modules [20]:

Property	GaAs (APG-81)	GaN-on-SiC (APG-85)	Improvement
Bandgap	~1.4 eV	~3.4 eV	2.4x
Breakdown Field Strength	~0.4 MV/cm	~3.3 MV/cm	~8x
Power Density	~1.5 W/mm	5-12 W/mm	3-8x
Power Added Efficiency	25-40%	50-65%	~1.5-2x

Sources: Qorvo GaN/GaAs Analysis [21], Military Embedded Systems [22]

¶ AN/APG-85 -- Operational Improvements

The AN/APG-85, also developed by Northrop Grumman, is intended for F-35 Lot 17 and subsequent production lots [23]:

Detection Range: Estimated ~50% increase over APG-81
SAR Resolution: Sub-meter capability through ultra-wideband operation
Electronic Warfare: Massively increased burn-through capacity
LPI: Ultra-wideband spreading reduces spectral power density

¶ TR-3 Dependency

The full potential of the AN/APG-85 depends on the successful integration of the Technology Refresh 3 (TR-3) computer infrastructure. TR-3 software stabilization is ongoing until at least 2026 [24].

¶ Strategic Context

The Chinese J-20 features the Type 1475 AESA radar with an estimated 2,000-2,200 TRMs in a larger aperture [25]. The AN/APG-85 is the answer to this physical disadvantage: since the F-35 cannot enlarge its nose cone, it must increase the power per module.

¶ Implication for Switzerland

According to current knowledge, the Swiss F-35As will be delivered with the AN/APG-81, not the AN/APG-85 [26]. This results in an estimated 33% lower initial detection range compared to APG-85-equipped allies.

¶ 5. Armament

The F-35 has internal and external weapon stations, the use of which directly affects the stealth signature [27].

¶ Internal Weapon Bays

F-35A/C: 2 bays, dimensioned for weapons of the 2,000-lb class
F-35B: 2 bays, somewhat smaller dimensions
Standard Loadout: 4x AIM-120 AMRAAM (air-to-air) or 2x AIM-120 + 2x GBU-31 JDAM (multirole)

¶ Sidekick Adapter

Starting from Lot 15, the Sidekick adapter enables the internal carriage of 6 instead of 4 AIM-120 AMRAAM in the F-35A/C variants [28]. The adapter is not compatible with the F-35B.

¶ External Pylons

6 external stations (3 per wing) with a total payload capacity of up to 8,160 kg (18,000 lbs) [27]. The use of external pylons significantly increases the radar cross-section.

¶ "Beast Mode"

Maximum external loading at the expense of stealth characteristics. Typical for scenarios with established air superiority.

¶ Current and Planned Weapon Integration

Weapon	Type	Status
AIM-120D AMRAAM	BVR air-to-air	Operational
AIM-9X Sidewinder	WVR air-to-air	Operational
GBU-31/32 JDAM	GPS-guided bomb	Operational
GBU-39 SDB I	Small Diameter Bomb	Operational
GBU-53/B StormBreaker	Tri-mode guided bomb	Operational
AGM-154 JSOW	Standoff glide bomb	Operational
AIM-260 JATM	Long-range air-to-air	In development (Block 4)
AGM-88G AARGM-ER	Anti-radiation missile	Internal integration planned
JSM (Joint Strike Missile)	Anti-ship/land attack	Norway/Australia

¶ 6. Stealth Technology

The stealth characteristics of the F-35 are based on several complementary technologies [29].

¶ Radar Cross-Section (RCS)

The estimated RCS of the F-35 is ~0.001-0.01 m² in the frontal hemisphere -- comparable to the size of a golf ball [30]. This value applies to X-band frequencies, as used by most tactical radars.

¶ Airframe Shaping

Edge Alignment: All edges (wing edge, tail edge, bay doors) are aligned to a few common angles to deflect radar energy in predictable directions
Continuous Curvature: No sharp transitions in the airframe geometry
Sawtooth Panels: Maintenance panels with sawtooth edges to scatter edge reflections

¶ Radar Absorbing Materials (RAM)

The F-35 uses Fibermat technology -- radar-absorbing materials baked directly into the outer skin [29]. Compared to the F-22 with glued-on RAM coatings, this is more corrosion-resistant and requires less maintenance.

¶ Diverterless Supersonic Inlet (DSI)

Instead of a conventional splitter plate, the F-35 uses a compression bump in front of the engine inlet [31]. Advantages:

~30% weight savings compared to conventional inlets
Elimination of the splitter plate as a radar reflector
Functions up to Mach 2.0 (tested on a modified F-16, December 1996)

¶ Luneburg Lens Reflectors

For peacetime flights and exercises, 4 Luneburg lens reflectors (2 on top, 2 on bottom) are attached, which intentionally increase the RCS [32]. They are removed for combat missions.

¶ Limitations

Against VHF radars (Very High Frequency, wavelength ~1-3 m), stealth aircraft like the F-35 are significantly more visible due to resonance effects [33]. Russian systems such as the Nebo-M specifically exploit this.

¶ 7. Sensor Fusion

Sensor fusion is the heart of the F-35 and the most important differentiator compared to fourth-generation fighter jets [34].

¶ Fusion Engine

All sensor data -- radar (APG-81), infrared (DAS, EOTS), electronic intelligence (ASQ-239), and data links (MADL, Link-16) -- are correlated in a central fusion engine and linked into a unified tactical situational picture [34].

¶ Tiered Data Approach

Tier 1: Data from the aircraft's own sensors
Tier 3: Fused data incorporating information from allied platforms via data links

¶ Panoramic Cockpit Display (PCD)

The 50x20 cm touchscreen display (20x8 inches) replaces conventional individual instruments and shows the fused situational picture in configurable views [35].

¶ Gen III Helmet Mounted Display System (HMDS)

Developed by Collins Aerospace (RTX) and Elbit Systems, the Gen III helmet enables [36]:

30x40-degree field of view with DAS see-through (the pilot can see through the aircraft)
Integrated night vision
Weapon control via gaze direction
Augmented reality overlays with tactical information
Over 3,000 systems delivered (as of: February 2024)

¶ Paradigm Shift

The F-35 does not primarily operate as a kinematic weapons platform but as a sensor node in a networked "Kill Web" [37]. The ability to absorb, process, and distribute information is operationally more significant than speed or maneuverability alone.

¶ 8. Communications -- MADL, Link-16, SATCOM

¶ MADL (Multifunction Advanced Data Link)

MADL is the stealth-optimized data link of the F-35, operating in the Ku-band with directional phased-array antennas [38]:

LPI/LPD: Low Probability of Intercept/Detection through directional beam characteristics
Data Rate: Significantly higher than Link-16
Limitation: Only usable between F-35s; incompatible with F-22 (IFDL) and legacy platforms

¶ Link-16

The standardized NATO data link for broad interoperability [39]:

Omnidirectional (not stealth-optimized)
Compatible with virtually all NATO platforms
Lower data rate than MADL

¶ The Interoperability Problem

F-35 (MADL) and F-22 (IFDL) cannot communicate directly with each other [39]. Solution approaches:

U-2S as Airborne Gateway: Demonstrated in 2021 -- the U-2 translates between MADL, IFDL, and Link-16 [40]
Open Systems Gateway (OSG): Tested at NATO Ramstein Flag 2025 -- MADL-to-Keystone translation for ground artillery [41]
DAGGR-2: Multi-protocol gateway with SATCOM integration (commercial via Starlink/Intelsat) [42]

¶ 9. Software -- Block Upgrades, ALIS/ODIN

¶ Block 4 Modernization

The Block 4 modernization originally encompassed 66 new capabilities but has been reduced due to massive delays and cost overruns [43]:

Parameter	Originally Planned	Current Status (2025)
Completion	2026	2031+
Cost	~$12 billion	~$18+ billion (+$6 billion over budget)
Capabilities	66	Reduced to "subset"

Source: GAO-25-107632 [43]

¶ Technology Refresh 3 (TR-3)

TR-3 replaces the legacy Integrated Core Processor (ICP) with a new system featuring [35]:

25x computing power compared to TR-2
New Panoramic Cockpit Display
Support for AN/APG-85 and Block 4 capabilities

Chronology of Delays:

2023-2024: Delivery pause due to unstable TR-3 software [44]
July 2024: Acceptance of a "truncated" software version to resume deliveries
2024: Average delivery delay of 238 days [43]
2026 (planned): Full operational test of the TR-3 configuration [24]

¶ ALIS and ODIN

ALIS (Autonomic Logistics Information System) was the original maintenance information system of the F-35 with severe problems [45]:

Unreliable diagnostics
Security vulnerabilities
Hardware weight: ~363 kg (800 lbs) per base kit

ODIN (Operational Data Integrated Network) replaces ALIS as a cloud-based system [45]:

Hardware reduction to ~64 kg (140 lbs)
Cloud-based architecture
Improved data access and analytics

¶ Block 5

Already in planning as the successor to the Block 4 modernization with additional capability enhancements [46].

¶ 10. Electronic Warfare -- AN/ASQ-239 Barracuda

The AN/ASQ-239, developed by BAE Systems, is the integrated electronic warfare system of the F-35 [47].

¶ System Architecture

10 RF antennas in the leading edges of wings and tail for 360-degree coverage
Multispectral Capabilities: RF and IR spectrum
Heritage: Evolution of the F-22 system AN/ALR-94

¶ Capabilities

Radar Warning: Detection and classification of hostile radar emissions
Passive Geolocation: Locating emitters across a broad EM spectrum without own emission
Countermeasures: Electronic jamming and deception
Integration: Full fusion with APG-81/DAS/EOTS for a correlated threat picture

¶ Block 4 Upgrade: DTIP

BAE Systems is developing the Digital Channelized Receiver Techniques Generator (DTIP) [48]:

Smaller form factor
Reduced power requirements
Space for future upgrades
Development contract: 493 million USD, production contract: 491 million USD

¶ Fleet Status

Over 1,200 AN/ASQ-239 systems were delivered by the end of 2024 [47]. BAE Systems is investing 100 million USD in a new manufacturing facility (7,400 m²) with AI-powered automation and a capacity of 11 systems per month [49].