BLU-3/B Submunition

1. Overview

The BLU-3/B is a United States anti-materiel and anti-personnel, high-explosive fragmentation submunition widely known by the nickname “Pineapple” due to its distinctive appearance when its six spring-loaded drag vanes are deployed. Developed during the late 1950s and early 1960s, the BLU-3/B saw extensive combat use during the Vietnam War and remains one of the most recognizable Cold War-era cluster submunitions. It continues to pose a significant UXO threat in Southeast Asia decades after its deployment.

Safety Note: All ordnance should be considered dangerous until proven safe by qualified EOD personnel. Unexploded BLU-3/B submunitions retain their full lethality and should never be handled by untrained individuals.

2. Country/Bloc of Origin

  • Country: United States of America
  • Era: Late 1950s–1960s development; combat use from the early 1960s onward
  • Manufacturer: Multiple U.S. defense contractors
  • Distribution: Used primarily by U.S. forces; also supplied to allied nations during the Vietnam War era

3. Ordnance Class

  • Type: Submunition (bomblet)
  • Role: Anti-materiel / anti-personnel fragmentation
  • Delivery Method: Air-dropped via dispenser systems (SUU-7 series and SUU-14 series dispensers), released as components of CBU-2 and CBU-14 cluster bomb units

4. Ordnance Family / Nomenclature

  • Official Designation: BLU-3/B (Bomb Live Unit-3/B)
  • ASETDS Classification: BLU (Bombs, Live Unit)
  • Common Names: “Pineapple bomb,” “Pineapple bomblet”
  • Practice Variant: BLU-28
  • Parent Systems:
    • CBU-2A (SUU-7/A dispenser carrying 360 BLU-3/B)
    • CBU-2A/A (SUU-7A/A dispenser carrying 406 BLU-3/B)
    • CBU-2B/A (SUU-7B/A dispenser carrying 409 BLU-3/B)
    • CBU-2C/A (SUU-7C/A dispenser carrying 409 BLU-3/B)
    • CBU-14/A (SUU-14/A dispenser carrying 114 BLU-3/B)
    • CBU-14A/A (SUU-14A/A dispenser carrying 114 BLU-3/B)

5. Hazards

  • Primary Hazard: High-explosive fragmentation. Detonation propels approximately 250–300 embedded steel balls at lethal velocity
  • Blast Effect: Secondary blast effect from the RDX/Cyclotol explosive charge
  • Sensitivity: Impact-fuzed; the submunition is designed to detonate upon contact with any surface. Unexploded items may be extremely sensitive to movement, vibration, or handling
  • UXO Considerations: The BLU-3/B has a significant dud rate. Millions of these submunitions were deployed in Southeast Asia, and substantial numbers failed to function on impact. These UXO items retain full lethality and are extremely hazardous. The fuze mechanism may have partially armed, leaving the submunition in a highly sensitive state
  • Environmental Degradation: Corrosion of the aluminum body and zinc alloy fuze components over decades may increase sensitivity or cause unpredictable behavior
  • Kill Radius: Effective fragmentation radius of approximately 5–10 meters for personnel casualties; steel balls can cause injury at greater distances
  • Special Hazard: The small size and sometimes colorful appearance of the BLU-3/B make it attractive to children, who may mistake it for a toy—a persistent humanitarian concern in post-conflict areas

6. Key Identification Features

  • Height (body only): 4 inches (101.6 mm)
  • Diameter: 2.7 inches (68.6 mm)
  • Height (vanes deployed): 6.8 inches (172.7 mm)
  • Weight: Approximately 1.73 lbs (785 g)
  • Shape: Cylindrical body with rounded top; six spring-loaded drag vanes attached at the top that deploy radially outward, giving the characteristic “pineapple” silhouette
  • Body Surface: Distinctive pebbled or dimpled appearance caused by steel balls embedded in the aluminum/ZAMAK casting alloy body matrix
  • Color: Body painted yellow with gold-anodized drag vanes and cup. All markings in black
  • Fuze Location: Threaded into the base of the body
  • Cup Assembly: Aluminum alloy cup crimped to the fuze, visible at the base
  • Materials: Body is aluminum/ZAMAK alloy with embedded steel balls; vanes are steel; nester is plastic (Bakelite); fuze components are brass, zinc alloy, and steel
  • Markings: Lot number and date of manufacture typically stenciled on the body in black

7. Fuzing Mechanisms

  • Fuze Type: Integral impact fuze with escapement delay mechanism
  • Arming Sequence:
    1. Upon ejection from the dispenser, the airstream strips the spring tab from the body
    2. Removal of the spring tab releases the safety strap
    3. The safety strap is ejected, allowing the six drag vanes to deploy outward under spring pressure
    4. Vane deployment releases the spring-loaded cup to move forward, withdrawing the firing pin from the arming slide cavity
    5. In late-model bombs, vane deployment also releases a spring-loaded safety pin, freeing the arming slide
    6. The drive spring moves the arming slide to align the detonator, lead charge, and firing pin
    7. An escapement mechanism provides a brief delay in arming slide alignment
    8. The bomb is now armed
  • Trigger Method: Impact-initiated. Upon striking any surface, the cup drives the firing pin into the aligned detonator, initiating the explosive train
  • Self-Destruct: None. The BLU-3/B has no self-destruct, self-neutralization, or time-delay deactivation features
  • Anti-Handling: No dedicated anti-handling device, but unexploded items with partially armed fuze mechanisms are extremely sensitive to any disturbance

8. History of Development and Use

  • Development: The BLU-3/B was developed in the late 1950s as part of U.S. Air Force efforts to create effective area-denial and anti-personnel weapons for air delivery. The design prioritized simplicity, low cost, and reliable fragmentation effect
  • Vietnam War: The BLU-3/B saw its most extensive combat use during the Vietnam War, where it was deployed in vast numbers by U.S. Air Force and Navy aircraft over Vietnam, Laos, and Cambodia from the early 1960s through the early 1970s. Delivered via CBU-2 and CBU-14 cluster bombs, millions of BLU-3/Bs were dropped during the conflict
  • Delivery Platforms: The CBU-2 and CBU-14 systems were employed by a wide range of tactical aircraft, including the F-4 Phantom, F-100 Super Sabre, F-105 Thunderchief, A-1 Skyraider, A-4 Skyhawk, and A-37 Dragonfly
  • Humanitarian Impact: The BLU-3/B is one of several submunition types that continue to cause civilian casualties in Laos, Vietnam, and Cambodia decades after the end of hostilities. Laos is the most heavily cluster-munition-affected country in the world, with an estimated 80 million submunitions failing to detonate during the war
  • Obsolescence: The BLU-3/B was succeeded by more advanced submunition designs (BLU-24, BLU-26, BLU-61, BLU-63, BLU-97, etc.) and is no longer in active U.S. military inventory
  • Current Status: Obsolete in production and service. Remains a significant UXO threat in former conflict zones

9. Technical Specifications

ParameterSpecification
DesignationBLU-3/B
TypeAnti-materiel/anti-personnel fragmentation submunition
Height (body)4 in (101.6 mm)
Diameter2.7 in (68.6 mm)
Height (vanes deployed)6.8 in (172.7 mm)
Total Weight~1.73 lbs (785 g)
Explosive Fill~0.4 lb (165–180 g) RDX or Cyclotol (70/30 RDX/TNT)
Fragmentation~250–300 embedded steel balls
Body MaterialAluminum/ZAMAK casting alloy with embedded steel
Fuze TypeIntegral impact fuze with escapement delay
ColorYellow body, gold-anodized vanes and cup
Practice VariantBLU-28
Dispenser SystemsSUU-7 series, SUU-14 series

10. Frequently Asked Questions

Q: Why is the BLU-3/B called the “Pineapple”? A: The nickname derives from the submunition’s appearance when its six spring-loaded drag vanes are fully deployed. The vanes extend outward from the cylindrical body, creating a silhouette that resembles a pineapple.

Q: What gives the BLU-3/B its pebbled surface texture? A: The body is manufactured using a casting process that embeds approximately 250–300 steel balls into an aluminum/ZAMAK alloy matrix. These balls create the visible dimples on the outer surface and serve as the primary fragmentation upon detonation.

Q: How does the BLU-3/B compare to the BLU-26/B? A: Both are anti-personnel fragmentation submunitions used during the Vietnam War, but they differ significantly. The BLU-26/B (the “guava bomb”) is a smaller, spherical, spin-armed submunition containing approximately 300 steel balls in 85g of Cyclotol, delivered via the CBU-24 system. The BLU-3/B is larger, heavier, fin-stabilized (vane drag), and impact-fuzed. The BLU-26/B had a different arming mechanism (spin-armed, spin-decay fired) compared to the BLU-3/B’s direct impact fuzing.

Q: What is the BLU-3/B’s dud rate? A: Precise dud rate figures for the BLU-3/B are not consistently published, but cluster submunitions of this era are generally acknowledged to have failure rates ranging from several percent to significantly higher under adverse conditions (soft ground, water, dense vegetation, low release altitude). Given the millions deployed, even a modest failure rate resulted in enormous numbers of unexploded submunitions.

Q: Why doesn’t the BLU-3/B have a self-destruct feature? A: The BLU-3/B was designed in an era before self-destruct or self-neutralization features were standard requirements for submunitions. The design philosophy prioritized simplicity, reliability, and cost-effectiveness. The absence of self-destruct capability is a major factor in the persistent UXO problem caused by these weapons.

Q: Is there any risk in approaching a BLU-3/B found in the field? A: Extreme risk. An unexploded BLU-3/B may have its fuze in a partially armed state, meaning any movement, vibration, or contact could complete the arming sequence and trigger detonation. Decades of environmental exposure may have further degraded safety mechanisms. These items must be reported to authorities and left in place for qualified EOD personnel to address.

Q: How many BLU-3/Bs were carried in a single cluster bomb? A: The loadout varied by dispenser type. The CBU-14/A and CBU-14A/A carried 114 BLU-3/Bs each using the SUU-14 series dispenser, while the CBU-2 series carried 360–409 BLU-3/Bs using the SUU-7 series dispenser.

Q: In which countries are BLU-3/B UXO still found? A: BLU-3/B remnants and UXO are primarily found in Vietnam, Laos, and Cambodia. Laos is the most heavily affected country. These items are also found on former U.S. military training ranges worldwide.