This post is part of the Defending Iran Project, accessible through this link.
Until the advent of marine nuclear propulsion in the 1950s, most submarines were, in effect, submersibles that primarily operated on the surface and briefly operated in a submerged state. Iran’s approach to employing its longer-range ballistic missiles can be productively understood as the opposite of how most submarines were employed prior to the advent of nuclear-powered submarines in the early Cold War. That is, Iran’s longer-range ballistic missile launchers and their associated missiles, including reloads, primarily remain underground, and briefly exit Iran’s heavily protected underground missile bases to operate outside so as to prepare ballistic missiles for launch, launch said ballistic missiles, and afterward return inside the underground missile bases—“submerge”—so as to reload, and more generally await orders to undertake another ballistic missile launch.
The pre-nuclear propulsion submarine analogy is also analytically productive for another reason. Even the latest diesel-electric submarines have to regularly operate at periscope depth so as to raise a snorkel (prior to the increasingly widespread use of snorkels toward the end of the Second World War, submarines had to fully surface so as to run their diesel engines). Even the latest diesel-electric submarines can be more readily detected when operating at periscope depth so as to run their diesel engines and, in so doing, recharge their electric batteries. The concept of a (submarine) indiscretion rate refers to the percentage of time that a non-nuclear-powered submarine must operate at periscope depth and run its diesel engines to recharge its batteries during a deployment. To reduce their exposure to threats and enhance their survivability, commanders of submarines without nuclear propulsion want to minimize the time they (unavoidably) have to spend at periscope depth, which is to say minimize their indiscrtion rate during a deployment.
The crews of Iran’s longer-range ballistic missiles and their parent units encounter much the same indiscretion rate dynamic as their counterparts who operate submarines not equipped with nuclear propulsion, whether in Iran or in any other country. Iran’s ballistic missile launch crews must, for all practical intents and purposes, exit the considerable safety of Iran’s underground missile bases so as to prepare ballistic missiles for launch, launch said ballistic missiles, and afterward return inside the underground missile bases—“submerge”—so as to reload, and more generally await orders to undertake another ballistic missile launch. As with the submarine analogy, Iran’s ballistic missile launch crews want to minimize the amount of time that they have to spend outside of the safety of their underground missile bases.
Indiscretion Rates and Liquid-Fuel Vs Solid-Propellant Ballistic Missiles
When it comes to Iran’s liquid-fuelled ballistic missiles, specifically those of R-17 Elbrus (i.e., “Scud”) heritage, including the longer-range Ghadr family, which combust liquid kerosene-type fuel with an oxidizer, the liquid fuel is, for all practical intents and purposes, not storable, and the missiles must be fuelled before use/launch. Fuelling is preferably undertaken outside, given the hazards that the liquid fuel combination poses to the crews, not least in an indoor setting of an enclosed space such as an underground missile base. While fuelling outside is preferable in terms of avoiding accidents and, failing that, mitigating the damage and casualties resulting from an accident during refuelling, it necessarily increases the indiscretion rate of Iran’s ballistic missile launch crews operating liquid-fuelled ballistic missiles (excluding those of the Khorramshahr family, which employ a different type of liquid fuel that is storable). As demonstrated in the June 2025 Iran-Israel War and over the course of the 2026 American and Israeli war against Iran, American and Israeli military aircraft, whether crewed or uncrewed, can be lying in wait outside Iran’s underground missile bases (among other ways to target Iran’s ballistic missile launchers outside of the underground missile bases). To lower the indiscretion rate of Iran’s liquid-fuelled ballistic missile launchers and associated crews, Iran is understood to be fuelling its liquid-fuelled ballistic missiles underground despite the major risks that doing so in an enclosed space poses in terms of the safety and, in effect, the survivability of all the personnel, launchers, and missiles stored within an enclosed underground missile base.
When it comes to Iran’s solid-propellant ballistic missiles, including those of the Kheibar Shekan family, the solid propellant is storable, and the missiles do not need to be refuelled prior to launch. The launchers associated with Iran’s solid-propellant ballistic missiles can be simply driven outside an underground missile base and quickly prepared for launch and thereafter return inside to reload.
There are trade-offs when it comes to liquid-fuel vs solid-propellant ballistic missile technology, not least for Iran. While solid-propellant ballistic missiles do not need to be fuelled prior to launch and are, as such, fairly safe to store underground, casting solid-propellant rocket motors is a hazardous activity and is, therefore, almost always undertaken above ground. Given the above, Israel, and now the United States, have been far better-positioned to degrade, if not suspend, Iran’s ability to manufacture solid-propellant ballistic missiles. In contrast, Iran appears to retain the ability to produce liquid-fuelled ballistic missiles, specifically those of the “legacy” and broadly outdated Ghadr family. It is important to note that Iran has reportedly placed greater emphasis on ballistic missiles of the Ghadr family since October 2024, despite the limitations of these “legacy” ballistic missiles relative to Iran’s newer solid-propellant ballistic missile designs.
The key point here is that solid-propellant ballistic missiles are, all things considered, the better option for Iran going forward, certainly as an alternative to non-storable liquid-fuel designs such as those of the Ghadr family, when it comes to lowering the indiscretion rate for Iran’s ballistic missile force, but there are highly pertinent Iran-specific factors at play which greatly increase the appeal of liquid-fuelled ballistic missiles for Iran, notwithstanding how non-storable liquid-fuels either result in higher indiscretion rates or, alternatively, pose greater risks of major damage resulting from accidents while fueling ballistic missiles within Iran’s underground missile bases.
Other Ways to Lower the Indiscretion Rate for Ballistic Missile Launchers
While a greater reliance on solid-propellant ballistic missiles amounts to one way to lower the indiscretion rate for Iran’s ballistic missile launchers operating out of underground missile bases, there are other ways to go about this, including ways to (further) reduce the indiscretion rate for Iran’s solid-propellant ballistic missile launchers. The key issue is to increase the number of ballistic missiles that a launch crew and associated launcher can launch per “sortie”—during every (preferably brief) deployment outside the safety of the underground missile base. This requires ballistic missile launchers that can launch more than one ballistic missile at a time. Needless to say, this does not lower the indiscretion rate for a given launcher and launch crew during a given “sortie,” but it can reduce the total number of “sorties” that an underground missile base must generate over a given timeframe, and this has the effect of functionally lowering the “aggregate indiscretion rate” over the course of a war, all else being equal.
Most of Iran’s ballistic missile launchers can only launch a single ballistic missile at a time, which is to say per “sortie.” This is particularly the case with respect to Iran’s longer-range ballistic missiles, that is, the launchers associated with ballistic missiles that have a maximum range of 1000 kilometers or more. This reflects the considerable size and weight of such Iranian ballistic missiles, including the quite large warheads that many such designs are equipped with in part to partially compensate for inaccuracy when equipped with a conventional high explosive-fragmentation warhead.
With respect to Iran’s “legacy” liquid-fuelled Ghadr family, which has a diameter of 1.25 meters, it is simply not possible for a reasonably sized launcher to transport and launch more than one such ballistic missile at a time. When it comes to smaller and comparatively shorter-range ballistic missiles, such as those of the related “legacy” liquid-fuelled Qiam family, which have a diameter of 0.88 meters, it is, however, possible to design a launcher that can carry two such missiles at a time. As the following images indicate, Iran has already done so.
With respect to Iran’s solid-propellant ballistic missiles, such as those of the Kheibar Shekan family, which includes the Fattah-1 and Fattah-2, a diameter of 0.81 meters makes it possible to design a launcher that can carry two such missiles at a time. As the following images indicate, Iran has already done so.
Other extant Iranian long-range ballistic missiles, namely the (storable) liquid-fuelled Khorramshahr family, and the solid-fuelled Haj Qasem design, are simply too large and/or heavy for a single trailer-type launcher to carry more than one of the aforementioned ballistic missiles at a time. It is worth noting that Iran’s comparatively shorter-range ballistic missiles, including the ~700-kilometer-range Zolfaghar and the ~1000-kilometer-range Dezful, which are related solid-propellant designs with a diameter of 0.68 meters—to say nothing of even smaller and lighter diameter solid-propellant designs—can be used with launchers that can carry at least two such missiles at a time. While beyond the scope of this post, it is worth noting that Iran’s shorter-range ballistic missiles encounter the very same indiscretion rate dynamic.
It is also worth noting that the likes of the much smaller and lighter 456 mm diameter BM-250 and the 368 mm BM-120/Fath-360, which are relevant when it comes to attacking targets located in the Gulf Arab states, are particularly well-suited for use with launchers that can carry more than two such ballistic missiles at a time.
Iran’s Ballistic Missile Launcher Indiscretion Rates Going Forward
All things considered, there is considerable scope for Iran to significantly lower, or at least functionally lower, the indiscretion rates for its ballistic missile launchers and associated crews operating out of Iran’s underground missile bases by developing and deploying launchers that can carry at least two missiles at a time. As explained earlier, this will not be possible with the “legacy” liquid-fuelled Ghadr family ballistic missiles that Iran is likely to heavily rely on going forward, on account of the damage that Israel and the United States have done to Iran’s solid-propellant ballistic missile industrial base. It is also not practical with the likes of the (storable) liquid-fuelled Khorramshahr family and the solid-propellant Haj Qasem simply on account of size and/or weight. Needless to say, launchers that can carry two or more ballistic missiles at a time do not directly address the limitations and risks inherent to Iran’s preferred approach to operating long-range ballistic missiles from underground missile bases. It also does nothing to directly address the threat that American and Israeli aircraft, whether crewed or uncrewed, pose to Iran’s ballistic missile launchers and associated launchers when they unavoidably and necessarily leave the safety of the underground missile bases to launch ballistic missiles of any given type. Even so, the fact remains that the situation that Iran faces is far from hopeless, and that there is scope for adaptation.
It is important to note that Iran itself unveiled trailer-type launchers capable of carrying two Qiam family or two Kheibar Shekan family ballistic missiles well before the October 2024 exchange with Israel and the June 2025 Iran-Israel War, let alone the current American and Israeli war against Iran. This strongly suggests that Iranian military planners are well aware of this general dynamic, even if they may have pursued such launchers not to lower the indiscretion rate, or even through the use of an analytical construct borrowed from submarine operations, but to simply economize on manpower, which is to say expand the number of ballistic missiles that can be launched with a given launch unit without expanding headcount.